Thanks for all the comments so far. Some assumptions/approximations for the dynamic model: 1. The 'tibia' or shin length of the link is assumed to be the hypotenuse between the actual tibia length and ankle to cleat measurement. This is an approximation to make it work in the four bar analysis. Ankle flexion assumed constant. 2. Crank angular velocity assumed constant. This is imperfect as the crank vel varies with load in 1 rotation.
Eduardo Bueno What’s interesting is if you repeated that mathematical process with 10 different riders (or even the left hand side of the same rider) you’d more than likely get a different result. Again, it’s pretty easy with the right tools to measure the angles your study has extracted. Studies have shown that more elite riders have a tendency to drop the heel less in the first phase of the stroke. The pedal stroke dynamics of individual riders is learnt (by huge amounts of repetition) and is very individual in itself. The real world challenge for bike fitters is to allow for individual movement patterns and more often than not, asymmetries in those patterns.
@@JerrysScenicCycling I would imagine this to be the case indeed. Cleats position affects muscle recruitment. Far too forward requires more calf to stabilize the foot for pedaling. Another issue is the shoe. Sometimes, larger-size shoes are purchased to deal with wide feet. unfortunately further moving the cleat screw-in position forward (as opposed to buying actual wide-style shoes).
Lyan Villacorta Such an important point. I see so many bike fit clients who turn up with big shoes because they have wide feet. There are some great wide fit shoes on the market now, so if you have wide feet it’s really worth taking the time to get the right shoe. Different brands have different hole positioning relative to their last too. The first Fizik shoes that were released 10 years or so ago had holes REALLY far forward. Bont have them pretty far back. Do your homework before buying.
I switched from 172.5 to 165 cranks a few years back for the reasons you so ably have shown in your presentation. Your presentation is the best I have encountered so far on this topic and validates my decision to switch to shorter cranks. Good to know that moving seat forward also helps to open hip angle. Maybe you could have a look at oval chainrings too, another controversial topic. Cheers
Thanks Norman. There are lots of assumptions and its a simplified model. Mixing engineering and biological/chemcia/neurologicall functions will never truly align.
it's neat to see the benefits of shorter crank lengths and I'd be interested to see how this could be adapted for MTB use where shorter cranks have inherent value anyways- fewer pedal strikes/lower BB for cornering aggressively. I wouldn't be entirely surprised if this is the next portion of geometry that gets pushed to the practical limit (like head angle, bar length, top tube length and stem length already have).
When you said inertia, my ears pricked up. I am only 6'2" but my legs are massive (and long). I have gone from 175 to 172.5 cranks and have my seat slammed forward. I feel I get a more integrated comfortable feel. The problem is when im at battle speed, im often at 105 - 110rpm for long periods. This has got to take a tole on my huge legs. Interestingly the only time Iv been able to finish with the chain gang at the end, after 40 minute averaging 27mph, I was running 170 cranks on a single speed with a bigish gear.
@Alien On a Bike lol poor thing. It's people like you who get sheltered all the way across France, being dragged along by decent sized men up front. Only kidding I'm just jealous 🤣
This is a very interesting analysis thats is very well done, I understand the constant angle flection assumption as adding more DOF can drastically change the complexity of the analysis. One thing I was thinking whist watching is that muscles have different force production profiles depending on the amount of flection at the joint (amount of stretch on the muscle), and although such impediments as hip impingement is a first priority, to maximise performance with a force analysis, consideration to each muscles force production profile is needed for an accurate depiction. I have an inkling that the ratio of force production between the glutes and quads at their respective angles would contribute towards a total picture. Again great work, and thanks for the video.
Hi, thanks for the comment. You're completely correct I think. It just highlights how complicated an optimisation problem it is, there are sooo many variables.
Great video ! With the reduction of crank length, should your model not also increase the seat height since the maximum extension of the leg is correspondingly shortened when the shorter crank is a the bottom of the rotation? That would open up the hips even more.
It does but you must consider that as one raises the saddle the setback incrementally increases too if the axis point is fixed so if you bring the saddle forward your hip angle is the same.
Being a shorter rider (173cm) I changed from 170 cranks to 165 a few years ago, it changed my life on the bike. It isn't just about the 4 bar. Shorter cranks allow the saddle to be moved up and back a few millimeters, for the same closed hip angle as the longer cranks, which unloads the weight on the hands, in my case it stopped numbness in my hands.
Nice presentation. Other key points I would consider.... One of the major reasons given for shortening cranks is the theory that it helps in more endurance focused events where power outputs tend to be relatively steady state (again, IM distance triathlon is a good example). There isn’t a huge amount of scientific evidence to back this up, as anything that involves testing whether a bike fit or equipment change increases failure time is inherently really difficult to test (there are just too many other external factors that might influence fatigue rates). It is pretty easy to dynamically measure closed hip angle (most bike fit motion capture tools do this). It’s all very well measuring the angle (or calculating what it might be with a tool like CAD) but that doesn’t tell you what hip angle any given rider can cope with over the course of their chosen event. It is possible to measure how the rider’s centre of pressure moves in the saddle throughout the pedal stroke (the pelvis can become more unstable in cases where any link in the kinetic chain (hip, knee or ankle) reaches, or is close to reaching the limit of its range of motion). Changes in pelvic stability due to any bike fit change including crank length can also be assessed using Inertial Measurement devices (mini gyroscopes and accelerometers) attached to the pelvis. These are especially handy as they can be used out on the road, not just in the lab/fit studio. Another hugely important thing to consider (and this is where using CAD or such like really starts to struggle) is that the human body (even of a highly trained elite athlete) is far from being a perfect machine. Accurately measure knee, hip and ankle angles for 100 individual pedal strokes and you won’t see two pedal strokes the same. Throw into that mix that a key component of fatigue (as well as reduction in force production) is a loss of motor skills (the ability to fire the right muscles in the right order) and it’s easy to appreciate that rider motion can be very different at the end of a long ride than at the start. This is why we feel like we’re pedalling squares when heavy fatigue sets in. A practical way of testing what crank length might work for you is to find a bike fitter with a fit bike that allows seat angle, bar position and crank length changes to be made. Once a position is found that’s approaching “optimal” (sorry for using that word as I’m a firm believer in that it’s unlikely there is a single fixed position that’s actually optimal). Pedalling one legged while varying crank length (and altering seat height to maintain the same leg extension at each selected length) will give a good guide as to what length “works”. The rider should be able to maintain a fluid pedal stroke when riding at low cadence without having to excessively rock the pelvis. Most people have one side that’s more mobile than the other. The trend in bike fitting at the moment is towards practical outdoor testing. Expect to see more fitters offering the opportunity to test crank length changes out on the road as part of their bike fit services. Sorry for rambling. Hope this helps.
I am retired and have ridden for over 50 years on the road. I still get 50 to 70 miles a week most of the year. But I am old school and know little about the reasons for crank length change. Old school was you don't want your knee in front of the axle when your peddle is at the 3 o'clock position. But I can see the advantage of moving the seat forward and up. When you get you knee in front do you loose any watts in your out put power? I would think as you move forward you affectedly in-gauge the peddle stroke a bit latter. Thanks for the video. I need all I can get ,it's tought keeping up with the young. LOL Rick D.
This a very interesting presentation. Have you considered expanding your analysis to include consideration of how changing the angular sweep of the thigh effects the ability of the associated muscles to output power? The analysis seems to assume that the leg muscles will be able to cope with all the resulting angular sweeps equally well.
That would be really interesting to do. Im trying to formulate some inverse kinematic model to deal with this but would also need some electro-gram medical grade equipment!
sabamacx mathematics + physics = engineering ... excellent analysis - would be good to use a model like this to spec setup on bikes when purchasing online - shame that engineers are not listened to more - age old problem.
@@tobiasbouma4071 mathematical physics is usually studied in a mathematics department, or the theoretical branch of a physics department. It's not an engineering field.
@@sabamacx Being in the (MP) field myself, I'm definitely aware of that. I was just surprised at the way the equality was presented given my background, is all.
Interesting!, I feel a hobby project coming on that involves Blender 3D, an inverse kinematics rig of my legs to scale and my current bike with correct angles and then loads of tweaking, thanks!
I have found that shorter cranks are so much easier on my joints. I still ride hard in spite of needing two knee replacements. I absolutely cannot tolerate long cranks now. I would expect the same for someone with a bad hip as well
Excellent video. Love hearing the workings of someone who knows his stuff. Had a quick look through the title of previous videos to see if there's interesting stuff there. Saw the name Hambini so instantly subscribed.
I'm not sure about the observation that "torque doesn't matter because you can always change gears". Would it be more accurate to say that "pedal pressure" doesn't matter because it can be compensated by the gear selection. Let's say that I want to output 200 watts. With a smaller crank arm and similar pressure on the pedals, I would (?) have to spin faster in a larger gear at the rear in order to produce the same number of watts. Although the amount of "work" is the same, this doesn't change the fact that I am spinning (i.e., exerting pressure) thru a lever that is longer with a 172.5mm compared to a 165mm crank, which is the definition of "torque". The way humans are engineered, maybe the overall torque is similar when averaged over the pedal stroke - smaller cranks delivering the torque without the "peaks" of the longer cranks. But theoretically, if our power delivery was uniform throughout the stoke, wouldn't the longer cranks would have more torque?
Something may looks perfectly correct on paper, but in RL we have 3D space... how about changing Q-factor instead of crank length? In most cyclists pedals are not very well aligned with hips vertically by z-axis, obviously.
Great engineering here. I was looking for someone to do this using Adams with all forces. Matching the forces with the muscle fiber to show really fatigue. As small fiber will be fatigue faster with similar force compared to large one. Thanks. Enjoyed the video.
@PeakTorque Could You make a follow-up for this video, regarding how one should choose crank lenght? I'm 189 cm with 91 cm inseam (long limbs, shorter torso). I have both 172,5 mm and 175 mm, i "feel" that I can produce power more easily with shorter ones (even with such minor difference...).
It would be good if you did an analysis of why light bikes feel fast even though the acceleration of the bike plus rider is only 1-2%. I think it is because of the force or impulst which comes back through the seat and handlebars which is due to the lower inertia. I can be bothered working out the maths and I’d probably stuff it up
You start out with hip angle-but you seem not to be emphasizing KNEE angle-and opening that up is a big deal if you have knee pain or a knee injury. I went shorter and it was *way* better. I also moved to more of a midfoot cleat position and that also helped.
Excellent vid. I made one a few years ago trying to debunk the myth of 'longer cranks = more power', but your figures, calcs and schematics make it much clearer!
I have a problem with your logic of why taller riders don't need longer cranks. It seems obvious to me that if you scale _everything_ up by the same factor all of your angles will be the same, and all of your velocities and accelerations will be proportional (The same if you normalize them to the scale) If a rider is 10% bigger on a frame that's the same shape, but 10% larger, using cranks that are 10% larger, and the seat height, and reach to the handlebars are 10% larger, all of the angles will be identical. All of the velocities and accellerations will be 10% larger, because the whole system is 10% larger, but your graphs should be identical if scaled appropriately. Should a long legged rider with longer, often stronger, muscles be limited to a (proportionally) narrower range of motion to produce force through? That doesn't really seem logical to me. That's not to say, there aren't tall riders who couldn't benefit from shorter cranks if there's other reasons, but if you're going to analyse the linkages, you should at least see that we are already using proportionally "short" cranks at 175mm. Assuming identical proportions, a 165cm tall rider like your friend, on a set of 160mm cranks will have the same angles, and proportional accelerations and velocities to you or I (I'm also 194cm tall) riding 188mm cranks. Unfortunately, It's difficult and/or expensive to even try it, as the availability of longer cranks is very limited, and the bottom bracket height on most bikes makes it a little iffy too.
Great piece of work, thinking and visually attractive presentation. OK it's a model. There are assumptions. But it's interesting to see what can be derived from that, knowing that it's not a perfect repesentation of reality (yet... :-) ). Curious to see what your real world experiences are with the 165mm cranks. Look forward to a follow-up!
Bravo - separating fact from fiction! I'm adjusting my seat height and saddle position tomorrow! But I need your torque analysis - please. I'm 65yrs old, 186cm tall, recovering from covid pneumonia a year ago which totally sacked my lung capacity and muscle mass. About 4 months ago I changed my crank length from my traditional 170mm (sometimes 172.5mm) to 175mm crank. I use a hacked drive train (48/38/28t x 11-50t). I’m not a weight weeny by nature, but I have managed to reduce my Surly Straggler down to 21.6 lbs from 28.5 lbs with phat 38c tires. With the longer crank arm, I feel more power and can accelerate faster in shorter periods, and I can keep peddling through varied flats and steeper slopes more often and for longer periods of time. I watch my cadence and it's easier to keep it in the 85/95 PRM range. The biggest plus of all is I get outside and away from a trainer in a room watching a flat screen, which I hate. So far, I've regained about 75 percent of my former strength. My stamina is still the sh*ts though. I would really appreciate your crank length vs torque analysis. I understand what you said about crank length vs gearing, but I'm convinced a longer lever (crank arm) is a benefit across the entire gear range for sport riding vs endurance/road racing.
Do you know if 'effective seat tube angle more important than crank length' is still true to the same degree on say a S(52cm) frame rather than L/XL(~58cm)? - In my mind it would be less impactful the smaller the frame, right?
for the accerelation and speed study, did you use a constant bicycle speed or constant crank rotational speed, meaning usually with a shorter crank, omega would go up
Out of the saddle only 172.5's work best for me, leverage must relate to structure, I'm assuming hip width, the mechanical advantage doesn't change. Ymmv 🍺
Do you think there would be a model where all the measurements could be plugged in and that would generate the best system? To include seat angle, leg lengths...
Interesting you brought up empirical measurements vs. metric. A colleague mine is doing _his_ research masters in the study of number systems and whether different systems have intrinsic properties that have a benefit in solving particular problems. I don't know his conclusion yet because he hasn't finished but as I see it base 10 has no more significance than most other bases. It's just the number of fingers and thumbs we have. It only has 2 factors while base 12 has 4. The more factors the more numbers can be represented precisely. In that regard base 12 is superior.
Yes, but what _base_ is imperial in? (still base 10, but ignoring that...) 12 inches in a foot, 3 feet in a yard, 1760 yards in a mile. Yes, our number system is fairly arbitrary being base 10, but there's still something to be said for using exponents of a base unit, rather than arbitrary counts of base units and memorizing a bunch of conversion factors.
How does ST angle or more importantly , starting with correct seat angle for geometry of frame and saddle set back and height effect correct crank length , here ?
Very interesting and I agree with it. I have a few questions that you will have better knowledge of and may be able to help. Does the foot not count as a lever? Surely cleat placement would impact all of these angles? Would the longer cranks not be more efficient if the body can tolerate them? For example for the bike to travel the same distance, I think you would have to do more revolutions on shorter cranks than longer cranks, therefore more drivetrain resistance and muscles going through more cycles (muscle relaxation affecting contractions ability). Hope this makes sense as I've struggled with optimising crank length. Generally I like shorter.
Alexander Hardy No not really, because you have gears to compensate for that, but you do have a slower foot speed with shorter cranks so can increase your cadence.
Always use shorter crank for giving you better cadence, when in the last kms of a long ride your cadence will drop naturally. Having longer cranks will decrease the cadence even at the beginning... Even mtbiker are switching to shorter cranks. For the cleats lots of bikefitters are moving them back... Triathletes have them at the middle of the foot to reduce calf muscle fatigue for the running session
The 'tibia' or shin length of the link is assumed to be the hypotenuse between the actual tibia length and ankle to cleat measurement. This is an approximation to make it work in the four bar analysis.
@@LucaBonato You're talking as if "better" cadence always means faster. I generally ride with quite a high cadence on my 180mm cranks. yes, my cadence dropped a little, but so what? Now I'm spinning 95 instead of 100, but I've got a little more leverage, so I can push a slightly harder gear too.
So here’s a question if someone was running a large single speed chainring 50T would you run shorter (165-170) arms or longer for less fatigue and better power or larger for more torque?
You are measuring from horozontal not the actual hip and ignored the action hip extensors. The imbalance caused by steep seat tube angles is a problem.
I've switched to 165 from 170 a few days ago. When doing a steady 8-16mins interval around ftp, the heart rate was 2-4bpm lower than using 170. And one more thing I noticed that it is easier to push down the pedal stroke because the starting point on 4/5 o'clock position is a bit lower.
Since Pogacar has dropped down the crank lenght from 172,5 to 170 I think he has lost some power in the climbs. He pedals with more cadence in flats classics and climbs, but years ago like in the final TT when he won the Tour of France to Roglic, he seemed to have less cadence but more power in the climb, in fact he won 2 Tours with 172,5mm cranks. Jonas Vingegaard is running 172,5 and he is even a smaller rider 174 cm, and look how his knees go upper than Pogacar´s knees now. So I think that deppends of your style or riding as Jonas Vingegaars for example likes to have less cadence and going with more strength in comparison for example of Roglic who also goes with 170mm cranks but with a lot of cadence. I am saying that because nowadays it seems shorter cranks are better, but I dont thinks so, it is like a fashions, and it is not for everybody.. it depends of your riding style...
Huh....today I switched from 170 to 175mm and my first long ride just “felt” better. 6’ with ridiculously long legs, platform pedals, and oval chainring. Used to run 180mm, so....😶
@@ClockworksOfGL I'm 6' 1/2" with 37" inseam and also find 170 too short. 172,5 is ok, that is what I'm most used to. Now I got 177,5 on the road bike and 175 coming to the TT. The experimenting continues...
Glad I'm not the only one. I'm 6'4" also with very long legs for my height. I definitely prefer the 180mm cranks I'm running now to the 175mm I was using before. They feel better on my knees when I'm sprinting, too.
I have difficulty accepting crank length is not effecting torque, this video and others state that you manage that with gearing and cadence. I see two machines working, just like an engine and a gearbox. The engines is making power and gearbox is putting it to the ground, ignoring crank length i fel is like ignoring bore stroke in an engine saying it's all in the transmission 🤔 The transmission is a ratio device who needs power externally
If u would have only one gear, u would have less torque. But with gears u can overcome this by a higher cadians. Maybe a shorter crank length acts somewhat like adding a tooth to the chainring
Worst thing about this video was that it ended! Really informative and thoughtful analysis of something I’m currently trying to get my head around. Thanks 👍
FFT!!! Could you add a video for all us fast-tempo long distance for-fun-pleasure riders. Less so than this video for explosive-power-racing types !!!! I'd love to think I'm fast and unlike Alehandro I was still fast at 40 and now 43 I've lost power and now just enjoy zone 4 no zone 5's
2 key problems I have with this analysis are failure to adjust seat height with crank length and the acceleration analysis assuming consistent velocity. When crank length is reduced by any measure, if saddle height is adjusted such that the bottom of the pedal stroke remains consistent, the effective change at the top of the pedal stroke is doubled. Also, there are several studies that show that reducing crank length results in increased preferred cadence. This would mitigate some if not all of the acceleration difference we see in your graphs. I also suspect that most cyclist's have a preferred/threshold of force per pedal stroke, and this is why we see higher preferred cadence for higher wattage.
I was thinking the same thing regarding the lever x velocity; that the increased cadance to compensate for the shorter arm would mitigate (part of) the acceleration difference. Curious how much it actually is.
Been riding for 30+ years. Always had 170s, am 5' 7", and noticed that I always had trouble accelerating from a dead stop, or ever, as compared to my taller compadres. Switched to 165s about 10 years ago and, man, what difference! Changed everything. And now I know why. Thanks so much for this.
its because when your thigh or femur is slightly lower it will produce way more force compared to get femur being at 90 degrees relative to upper body. Its like doing half deadlifts. Also whenever I watch taller rider their knees never go up the same amount as it does on shorter riders. Not fair.
Fascinating study you’ve done here. I’m very interested in following your progress. My academic background was in Human Factors Engineering and Ergonomics many years ago before I started cycling. I have been searching for an analysis just like yours. I like that you also mentioned leg mass as well. I am about 185 cm tall with large feet (size 47), and big legs. I also have fairly long tibias. I do not use a power meter but I do get the feeling that I cycle better with shorter cranks. The joint angle I am concerned with is the knee. There is a very powerful fulcrum there as well and I want to continue to preserve my 65 year old knees. I haven’t measure power but is seems to me I am able to generate more power at the pedal with the more open knee angle a shorter crank provides. Knee angle and hip angle are related but I haven’t paid attention to hip angle. I look forward to seeing your next video on the subject. Thanks!
I touched on dynamics at high school, remember fluid dynamics in physics class. I remember we had to calculate the torque and kilowatts required for an oil pump to deliver X amount of litres per hour at a given RPM. The fluid viscosity was set and the pump volume per cycle was also set. Pretty simple with given data much harder to engineer.
As I aged, I noticed that my warm-up for rides to the point where I could accelerate with the group was taking longer and longer. I am 6'4" tall and have used 175 cranks forever. I decided to try 172.5's, and that warm-up period more or less disappeared. Also, my pedal stroke up very steep hills smoothed out. Since I am about to turn 79 (tomorrow) and over the last two years, my power has almost disappeared, so every little bit helps. Over the past 12 months I've ridden 5,000 miles and climbed 80,000 feet which is about one third my normal climbing (last winter destroyed many of the hill roads) I have been unable to easily find the climbs best suited to me. Plus, with my degradation of power, I am too slow to ride with the group and so have to ride solo much of the time. But the improvement in power with the shorter cranks. I am able to continue even on the worst sections, though I am crawling over the steep sections.
Watched this video and would like to comment on your CAD model/dynamic simulation. In that model the angle between your ankle and lower leg is held constant, which you do mention at approximately 12:25. For your CAD model what you should do is constrain the angle of the foot to the ground, not to the lower leg. If you watch riders from a side view you will see that through a full pedal rotation, the foot is held at 20-30 degrees to the road surface. This varies throughout the stroke, and if you could model this correctly in your CAD skeleton, you would see different results in hip angle especially at the top of the stroke (330°-60°). See if you can find videos of experienced cyclists on trainers from a side view and you will see what I mean.
5' 7" (30" inseam) and I find 170mm cranks too long. I've been experimenting with shorter kids bike cranks, 152mm to 130mm, and find that 1mm ends up equaling about 1RPM of perceived cadence. (85RPM @170mm feels like 103RPM @152mm) The cadence where I can hold my FTP at the lowest heart rate is about 95RPM. That seems to line up with the dynamic model that I should probably use 160mm cranks. Too bad they're such a PIA to find.
@@PeakTorque I managed to get some 160mm 105 Cranks. Instantly increased my average cadence by 8 rpm. Power is down a little because I'm not conditioned to the faster cadence. (Fast twitch fibers in the quads are on fire). Way more comfort, and simpler to find a good fit.
Good analysis. I ride long cranks (old school 185 and 180mm). Recently I have a bike with shorter (175mm) cranks. The feeling is very different. My second ride with the bike resulted in "exploded" legs after 75km. You really need to adjust to it timing wise. My cadence did not change (94rpm average). In several studies they changed crank length and tested in a short period of time. That would never give a good result.
The time spent reading or watching how to improve my performance normally yields a negative return on investment vs spending the time actually training. This video is an exception. It inspires informed experimentation which may indeed uncover flaws in my current setup. Being able to present significant ME theory to the point of almost sounding sexy is quite a testament to your overall skill set. 😊
I would love to see how an oval chainring plays into this equation and also the other interest would be how cadence speed would it should change to create the same output. Great clip.
By surveying some decent bike fitters… that fore aft seat position should not be used to open hip angle because moving seat forward means your torso can become unbalanced as it is more cantilevered over the bars.. this results in saddle sores and numb hands.. therefor fore aft position should be driven by balancing upper body weight.. I’ve experimented with this (and reach.. discovered that handlebar width increases reach!) and my numb hands and saddle sores are GONE!! Much better to use crank length since it doesn’t throw off everything else.
Noice! Have you considered or already done the 5 linkage version, adding in the ankle-to-cleat link? The whole "cleat under ball of foot" rule of thumb has also been subjected to actually doing the science and thinking about it from a biomechanical POV, with cleats being closer to the midfoot showing some real benefits, such as increased foot stability and reduced calf loads/fatigue.
I'm 69 years old, 180 cm tall. I have 2.5 cm longer legs and shorter torso than average for a male of my height. Usually ridden 172.5 mm as that's what the bikes came with. But my Specialized Steel Langster had shorter cranks (165mm?) and I absolutely loved it, rode it very hard up and down hills in traffic and in rural areas. I had a chance to get shorter cranks when my 2018 Ultegra cranks were recalled and replaced last year... but I forgot! Now about £250 to get shorter cranks and that is a long way my pension budget list of desirable items
Very interesting. One idea I’ve got about the limitations of short cranks is that you spend less time in the down stroke of the pedal (due to shorter range and higher RPM). This gives less time for RFD (rate of force development). RFD is basically how quickly and simultaneously your neuromuscular system can recruit high threshold motor units. To demonstrate this, flick your hand with your finger. Supporting the finger at the nail with your thumb gives time for RFD. If you try flick by just extending the finger un supported, you can’t generate as much force.
Secondly, overly long cranks would put you out of the range of motion where you have maximum Actin and myosin cross bridging. This would also limit your force production. Example, flex your wrist (bringing palm towards your forearm) and then try to clench your fist. You have less strength than wrist in a neutral position because you’ve pre shortened the muscle and put it out of the range of maximal cross bridges
So would shorter cranks be better as your legs would be closer to resting neutral position? I think of long cranks as having to do a deeper squat. I could squat way more weight if I didn't have to go down as far.
Alexander Hardy yeah, if you had unlimited time to generate force you can achieve the maximum force in a narrow range of Motion (like the top of a squat). But, because the pedal stroke is high velocity, a shorter range of motion reduces the time you have available to generate force (it takes time for your CNS to send the signals and activate all your motor units). Realistically though, I don’t know how much difference it makes between 165mm crank and 170. I think track riders tend to use shorter cranks and they achieve very high peak power output? However, they are very explosive athletes and do a lot of weight training so they would be very good at quickly generating high forces. It’s possible that as you decrease your explosive strength deficit (the difference between your maximum force to the max force you can generate in the time limits of a particular movement), shorter cranks would become more useful to you? If you have low RFD maybe you need a Lower cadence and longer pedal stroke? Sorry not very helpful there, just thinking out loud.
Very good, and yes people have many myths surrounding shorter cranks, but there is more; Shorter cranks require a higher seat position, this may be desirable for a person using aerobars to get the back flatter Shorter cranks means a slower foot speed, therefore you can increase your cadence easily, this may also be advantageous For track, 165mm is used for clearance, but they run many different fixed gears, so does it make that much of a difference? Your power remains the same as as you said, you have gears to compensate for the torque advantage at the crank, the whole action needs to be considered. Some proclaim shorter cranks are always better, but there is disagreement in the industry. It is clear that you need to study a number of factors as to what you are trying to achieve before making an adjustment. A “general” statement, (if there is such a thing relating to cranks) if using aerobars a shorter crank can be advantageous, for road riding it isn’t so important
at 5'7" with a 29" inseam i find the 165 cranks on a medium frame work for me because my upper body is long so i need to stretch out but the little engine needs those short cranks to spin well. i notice a huge difference between 165 and 172.5 here's the worst... when i was asking about this at a local bike shop ( B.S. shop more like it ) i was told in a dismissive tone ( 172.5 is standard. Same thing when i queried bar width. I didn't even buy my bike there!! Then again, it's Toronto where all shop owners have the attitude of they do not need your shitty money. 165 made the difference for me and I don't even know the math as well as you. I just feel it.
I went for 220mm cranks, from 200 originally then 215mm, reason being, for me they feel comfortable. Like having a nice stretch or walking with a longer stride. I do have a 39 inch inside leg length though.
Great video, very informative and I love the use of engineering to debunk cycling myths. Did you ever make the follow up video about force? I couldn't see it
I have a question regarding the the change to crank arm length: Why did you not change the seat height by the same amount? It is recommended to change the seat height by the same amount you change the crank length to reach the same effective seat height again. I see the value of isolating a variable in analysis, but in this case it does not seem correct to isolate this change when you will always change seat height at the same time. Further more so as in the next step you talked about the benefit of raising the saddle and setting it further forward. This would be the next logical step after reducing crank length anyway. Seeing bikefit as a system, where one parameter changes others at the same time, it seems to me, that it is not advisable to isolate changes for analysis.
Great analysis. I think the main problem is that road bikes are still way too conservative on their geometry. Crank length is one point - but the much larger problem is that road bikes seem archaic when it comes to findings on what is faster on mountainbikes, think Mondraker Forward Geometry or Pole bikes - mow more or less implemented in all bikes. Ideally we want much steeper seat tubes - maybe 76-77°, maybe even 78° as on Pole bikes (though then the more you use your bike for climbing - the steeper you like your seat angle), longer reach but shorter stems, and much slacker head angles (and yeah wheel base will rocket from the paltry 99cm to 110-115cm or so - notice enduro mountainbikes have arrived at 130cm already for a size large). The main problem is the handlebar width - going 10-20cm wider would likely be really beneficial fore most going uphill, but really inefficient in the wind. This would resolve a lot of too much weight on hands/shoulders problems. Someone really needs to think forward, forget UCI norms, and look at things that made mountainbikes fast. Then get people to train on a new geometry for some months and compare speed and comfort. Some things from the mountainbike side may not work on roadbikes (for sure no 75-80cm wide handlebars) but a lot will. To counter the slacker head angle and weight distribution - the chainstay length will need to grow too - however road bikes likely need much less weight on the front wheel vs mountainbikes - so shorter CS = less weight on your arms = more comfortable. And yeah if crankarms reduce in size, the long needed evolution of chainring sizes going smaller needs to continue too. Average Joes tend to run way too big rings up front instead of spinning faster and trying to choose a small ring that allows them never to drop below 80RPM on their steepest common climbs. It's crazy how conservate and stupid a lot of the bikefitting is on roadbikes - trying to fit people onto frame geometries that are simply wrong from the start. And yeah it needs a radical departure from the status quo. Most of bike fitting is simply an reaction to wrong bike geometries.
Agree, frame geometry needs to be looked at, seat tube angles are far too relaxed. I've always thought we should be far more over the BB in order to sync the lower body. I always slam my seat as fwd as I can and never have pain
When I was racing off road in the 90s, everyone was using 175+mm cranks, but being under 5.5 ft tall with short legs, I found 175 cranks just too long. I switched to 170s and never looked back.
Id like to see you do a force vs. Femur/Tibia angle at the pedals. That coupled with the crank length should give you the best idea of optimal crank length to run.
Love the analysis, but (I think you know) its not a 4 bar link...its a 5 bar link. I know you’ve intentionally made the ankle fixed in your model, but If you are ignoring the range of motion from the ankle then you are missing a key attribute. If (as in your CAD model) the foot to shin angle is static then from my analysis of many riders, they are wasting significant range of motion and not engaging the power of the calf/shin muscles in the power stroke. In my own tests, and tests with many customers, I can produce 20% more power through effective “ankling”. So I’d suggest the model needs updating, as Ankling does have significant impact on correct saddle height, power phasing, muscle load etc. which I believe will have impact on your analysis. Obviously foot length and cleat position will then make this more complicated ;-)
I'm one year late, but this is a truly fascinating comment - the 20% more power through effective "ankling" is an impressive number and I would love to get at least a rough idea of what this involves - some level of toe pointing to involve the calve muscles at the lower part of the stroke I presume but then perhaps heel dropping at the top too?
I went just recently over to 165mm cracks from 175mm cranks that I have used pretty much all my grown life. Well in the first two weeks if felt like the smaller circle you are pedaling in was so restrictive that I was about to change back. You got no power, and it feels like you are on a those tricycles if you remember those from your early childhood. But I noticed that I never ever had any pains or similar issues in the knees and the like, and even though I still am lacking in power it seems I am adapting to this as well. Oh yeah, I am 172 or 5,6 or 5,7 or something like that.
I'm running 155 rotor cranks at 6 ft 3 they are great for running of the bike. Maybe losing a little force but over longer tri distances the less stress on the hip flexers out way the trade in my opinion
A longer crank just means the more you have to pick your leg up to get a full rotation, so being longer in the legs doesn't really make that advantageous. It's like saying larger mtb riders should be on bigger wheels. Not true at all, merely that smaller riders can't always get the ideal geometry to fit around a larger wheelset. A large frame can have any size wheel it wants, a larger rider can have any size crank they want. I think the same goes for crank length.
@@Metal-Possum why don't we all just switch to 100mm cranks, and spin away at 180RPM on the little ring? If you run 160mm, you're just having to lift your legs higher.
nwimpney I know you mean this in an absurd way, but I think you’re onto something. 180rpm is hard for most people to sustain, regardless of crank length, because of the frequency at which muscles need to fire and relax. So the biomechanically ideal crank length (besides positional stuff) would probably be the one where the rider’s preferred foot speed and the rider’s preferred firing frequency meet. I’m not sure how you would determine either one, though.
Interesting. Never thought about it in terms of degrees/s of the femur. I have 175's and am considering 170's for less hip angle. But at age 60, I am more concerned about how raising the seat will then impact saddle to stem height and the changes I may have to make to the front end. One thing leads to another...... 😁😁
in my experience, it is all a matrix of bike geometry, body and adaption, and cycling environment ( eg. hilly, flats, urban, short circuits vs. endurance) - in other words, numbers (175, 170) are meaningless.
I'm 5'6 / 165cm with 29" inseam. I modified by machining two new positions on Shimano arms from 172.5 to 155mm. I also lifted my seat by about 15mm. The difference was compelling. For me, MUCH smoother and I stopped rocking on my seat. My Zwift output appears to have gained 5-10w at same heart rate. Too many geometry factors here for me to consider (or understand). My 'seat of the pants' mods tell me I'm OK with the new geometry.
Just by curiosity, have you taken into account the muscles that are engaged given the crank length? I reckon it might have some effect on power. Like muscles might flex just a bit more to get more juice out, or some crazy shit like that. Just a thought
Best quantitative explanation I have come across. My background is on robotics and controls. I’ve analyzed the Puma (swing, shoulder, elbow, spherical wrist) geometries “many years ago”. I have not come across a proper linkage/geometric analysis like you did here. Thanks for creating intelligent, analytical content!
Subjective comment: I’m 5’9” / 175 cm and in my late 50’s. I live on a small mountain range where my climbs average 5 to 9% with gradients of 14 to 18% common. I’ve had several road bikes in size 56 cm and they all came with 172.5 mm cranks. After reading and watching about crank length I went with 170 mm on my last bike purchase. I couldn’t be happier. The difference when climbing was immediately noticeable. I wasn’t straining as much, but I was spinning faster. My times going up remained about the same, but I feel better at the top. Thanks for the informative video.
Hi James I've always thought getting the right riding position is an art, but the science is all new to me. I would have immediately guessed that a longer lever / crank would make spinning easier, but I suppose that's where ergonomics comes in! Found your comment very interesting 👍🏾
Thanks,I shall follow with interest. Another aspect: what if you have different leg length's and/or variances in tibea/ femur? E.G: my right femur is 22 mm longer than left,while the right tibea is shorter. Overall my right leg is 37mm shorter. To complicate matters my right ankle has a fusion and alignment issues,making for complicated bio-mechanics.
Real world experience; Male, 177/2.5mm v 165mm height, height;177, long femur (52/48ratio, women legs). 45 years of riding and racing. Longer cranks are more fatiguing, as most long rides have long spells of 160 watt output, just spinning. So small circles are less fatiguing and more efficient due to the flattening of the curve (as shown). I discovered this years ago and my climbing improved ( 1hour plus road mountain climbs) again less chance of peddling in squares and using gears...Also moved saddle forward, more 130mm stem for stable mountain descending (which I love, completely changed the handling for the better), which again helped climbing in a smooth manner, revs the standard 75-80rpm (very few can rev at 90 efficiently and blow). This all came form that original ironman triathlete paper concerning 140mm cranks as an extreme, about 10 years ago.. Conclusion; less fatigue, better run off the bike, faster time.
Thanks for all the comments so far. Some assumptions/approximations for the dynamic model:
1. The 'tibia' or shin length of the link is assumed to be the hypotenuse between the actual tibia length and ankle to cleat measurement. This is an approximation to make it work in the four bar analysis. Ankle flexion assumed constant.
2. Crank angular velocity assumed constant. This is imperfect as the crank vel varies with load in 1 rotation.
See this for some information on the ankle rotation during the pedal stroke: cds-0.blogspot.com/2011/09/pedaling-model-i.html?m=1
Eduardo Bueno What’s interesting is if you repeated that mathematical process with 10 different riders (or even the left hand side of the same rider) you’d more than likely get a different result. Again, it’s pretty easy with the right tools to measure the angles your study has extracted. Studies have shown that more elite riders have a tendency to drop the heel less in the first phase of the stroke. The pedal stroke dynamics of individual riders is learnt (by huge amounts of repetition) and is very individual in itself. The real world challenge for bike fitters is to allow for individual movement patterns and more often than not, asymmetries in those patterns.
@@JerrysScenicCycling really interesting results, thanks for sharing.
@@JerrysScenicCycling I would imagine this to be the case indeed. Cleats position affects muscle recruitment. Far too forward requires more calf to stabilize the foot for pedaling. Another issue is the shoe. Sometimes, larger-size shoes are purchased to deal with wide feet. unfortunately further moving the cleat screw-in position forward (as opposed to buying actual wide-style shoes).
Lyan Villacorta Such an important point. I see so many bike fit clients who turn up with big shoes because they have wide feet. There are some great wide fit shoes on the market now, so if you have wide feet it’s really worth taking the time to get the right shoe. Different brands have different hole positioning relative to their last too. The first Fizik shoes that were released 10 years or so ago had holes REALLY far forward. Bont have them pretty far back. Do your homework before buying.
As soon as I heard PowerPoint, I was waiting for 'aged 5' to appear 😂. Crackin' vid 👍🏻
pen is working
"Let's put some numbers to it" thank you! The lack of data and sound reasoning behind most discussions/debates in cycling has driven me nuts!
I switched from 172.5 to 165 cranks a few years back for the reasons you so ably have shown in your presentation. Your presentation is the best I have encountered so far on this topic and validates my decision to switch to shorter cranks. Good to know that moving seat forward also helps to open hip angle. Maybe you could have a look at oval chainrings too, another controversial topic. Cheers
Thanks Norman. There are lots of assumptions and its a simplified model. Mixing engineering and biological/chemcia/neurologicall functions will never truly align.
it's neat to see the benefits of shorter crank lengths and I'd be interested to see how this could be adapted for MTB use where shorter cranks have inherent value anyways- fewer pedal strikes/lower BB for cornering aggressively. I wouldn't be entirely surprised if this is the next portion of geometry that gets pushed to the practical limit (like head angle, bar length, top tube length and stem length already have).
Don't forget the beer belly effect! For a lot of riders I see, reducing the hip angle means that the knees don't hit the gut LOL.
When you said inertia, my ears pricked up. I am only 6'2" but my legs are massive (and long). I have gone from 175 to 172.5 cranks and have my seat slammed forward. I feel I get a more integrated comfortable feel. The problem is when im at battle speed, im often at 105 - 110rpm for long periods. This has got to take a tole on my huge legs. Interestingly the only time Iv been able to finish with the chain gang at the end, after 40 minute averaging 27mph, I was running 170 cranks on a single speed with a bigish gear.
@Alien On a Bike lol poor thing. It's people like you who get sheltered all the way across France, being dragged along by decent sized men up front. Only kidding I'm just jealous 🤣
This is a very interesting analysis thats is very well done, I understand the constant angle flection assumption as adding more DOF can drastically change the complexity of the analysis.
One thing I was thinking whist watching is that muscles have different force production profiles depending on the amount of flection at the joint (amount of stretch on the muscle), and although such impediments as hip impingement is a first priority, to maximise performance with a force analysis, consideration to each muscles force production profile is needed for an accurate depiction. I have an inkling that the ratio of force production between the glutes and quads at their respective angles would contribute towards a total picture.
Again great work, and thanks for the video.
Hi, thanks for the comment. You're completely correct I think. It just highlights how complicated an optimisation problem it is, there are sooo many variables.
Great video ! With the reduction of crank length, should your model not also increase the seat height since the maximum extension of the leg is correspondingly shortened when the shorter crank is a the bottom of the rotation? That would open up the hips even more.
Martin Anderson very true 👍
1:30 and 16:30 mentions that.
It does but you must consider that as one raises the saddle the setback incrementally increases too if the axis point is fixed so if you bring the saddle forward your hip angle is the same.
Being a shorter rider (173cm) I changed from 170 cranks to 165 a few years ago, it changed my life on the bike.
It isn't just about the 4 bar.
Shorter cranks allow the saddle to be moved up and back a few millimeters, for the same closed hip angle as the longer cranks, which unloads the weight on the hands, in my case it stopped numbness in my hands.
Same here.
lol if you consider yourself short, idk what I am (165cm), even 51cm frames feel big to me
Nice presentation. Other key points I would consider....
One of the major reasons given for shortening cranks is the theory that it helps in more endurance focused events where power outputs tend to be relatively steady state (again, IM distance triathlon is a good example). There isn’t a huge amount of scientific evidence to back this up, as anything that involves testing whether a bike fit or equipment change increases failure time is inherently really difficult to test (there are just too many other external factors that might influence fatigue rates). It is pretty easy to dynamically measure closed hip angle (most bike fit motion capture tools do this). It’s all very well measuring the angle (or calculating what it might be with a tool like CAD) but that doesn’t tell you what hip angle any given rider can cope with over the course of their chosen event. It is possible to measure how the rider’s centre of pressure moves in the saddle throughout the pedal stroke (the pelvis can become more unstable in cases where any link in the kinetic chain (hip, knee or ankle) reaches, or is close to reaching the limit of its range of motion). Changes in pelvic stability due to any bike fit change including crank length can also be assessed using Inertial Measurement devices (mini gyroscopes and accelerometers) attached to the pelvis. These are especially handy as they can be used out on the road, not just in the lab/fit studio.
Another hugely important thing to consider (and this is where using CAD or such like really starts to struggle) is that the human body (even of a highly trained elite athlete) is far from being a perfect machine. Accurately measure knee, hip and ankle angles for 100 individual pedal strokes and you won’t see two pedal strokes the same. Throw into that mix that a key component of fatigue (as well as reduction in force production) is a loss of motor skills (the ability to fire the right muscles in the right order) and it’s easy to appreciate that rider motion can be very different at the end of a long ride than at the start. This is why we feel like we’re pedalling squares when heavy fatigue sets in.
A practical way of testing what crank length might work for you is to find a bike fitter with a fit bike that allows seat angle, bar position and crank length changes to be made. Once a position is found that’s approaching “optimal” (sorry for using that word as I’m a firm believer in that it’s unlikely there is a single fixed position that’s actually optimal). Pedalling one legged while varying crank length (and altering seat height to maintain the same leg extension at each selected length) will give a good guide as to what length “works”. The rider should be able to maintain a fluid pedal stroke when riding at low cadence without having to excessively rock the pelvis. Most people have one side that’s more mobile than the other. The trend in bike fitting at the moment is towards practical outdoor testing. Expect to see more fitters offering the opportunity to test crank length changes out on the road as part of their bike fit services.
Sorry for rambling. Hope this helps.
Cheers, great comment and insight.
A guru bike fit can adjust all these metrics.
bryn green Choose a fitter as opposed to a branded system when you’re looking at bike fit options.
I am retired and have ridden for over 50 years on the road. I still get 50 to 70 miles a week most of the year. But I am old school and know little about the reasons for crank length change. Old school
was you don't want your knee in front of the axle when your peddle is at the 3 o'clock position. But I can see the advantage of moving the seat forward and up. When you get you knee in front do you loose any watts in your out put power? I would think as you move forward you affectedly in-gauge the peddle stroke a bit latter. Thanks for the video. I need all I can get ,it's tought keeping up with the young. LOL Rick D.
This a very interesting presentation. Have you considered expanding your analysis to include consideration of how changing the angular sweep of the thigh effects the ability of the associated muscles to output power? The analysis seems to assume that the leg muscles will be able to cope with all the resulting angular sweeps equally well.
That would be really interesting to do. Im trying to formulate some inverse kinematic model to deal with this but would also need some electro-gram medical grade equipment!
@@PeakTorque would be most beneficial to this analysis, I;m sure
I mean, here's a years intro prep work for a sports physiology masters/phd here.
sabamacx mathematics + physics = engineering ... excellent analysis - would be good to use a model like this to spec setup on bikes when purchasing online - shame that engineers are not listened to more - age old problem.
@@dominicbritt they may not be listened to by management, but the customers listen. Which is frightfully effective.
@@dominicbritt Where does that place mathematical physics then? :D
@@tobiasbouma4071 mathematical physics is usually studied in a mathematics department, or the theoretical branch of a physics department. It's not an engineering field.
@@sabamacx Being in the (MP) field myself, I'm definitely aware of that. I was just surprised at the way the equality was presented given my background, is all.
Interesting!, I feel a hobby project coming on that involves Blender 3D, an inverse kinematics rig of my legs to scale and my current bike with correct angles and then loads of tweaking, thanks!
You're right, it needs inverse kinematics 😉
I have found that shorter cranks are so much easier on my joints. I still ride hard in spite of needing two knee replacements. I absolutely cannot tolerate long cranks now. I would expect the same for someone with a bad hip as well
Very good analysis, real food for thought, thank you. looking forward to the next one.
Excellent video. Love hearing the workings of someone who knows his stuff. Had a quick look through the title of previous videos to see if there's interesting stuff there. Saw the name Hambini so instantly subscribed.
I'm not sure about the observation that "torque doesn't matter because you can always change gears". Would it be more accurate to say that "pedal pressure" doesn't matter because it can be compensated by the gear selection. Let's say that I want to output 200 watts. With a smaller crank arm and similar pressure on the pedals, I would (?) have to spin faster in a larger gear at the rear in order to produce the same number of watts. Although the amount of "work" is the same, this doesn't change the fact that I am spinning (i.e., exerting pressure) thru a lever that is longer with a 172.5mm compared to a 165mm crank, which is the definition of "torque". The way humans are engineered, maybe the overall torque is similar when averaged over the pedal stroke - smaller cranks delivering the torque without the "peaks" of the longer cranks. But theoretically, if our power delivery was uniform throughout the stoke, wouldn't the longer cranks would have more torque?
Something may looks perfectly correct on paper, but in RL we have 3D space... how about changing Q-factor instead of crank length? In most cyclists pedals are not very well aligned with hips vertically by z-axis, obviously.
Love to see this for riding out the saddle.
Great engineering here.
I was looking for someone to do this using Adams with all forces.
Matching the forces with the muscle fiber to show really fatigue. As small fiber will be fatigue faster with similar force compared to large one.
Thanks. Enjoyed the video.
Adams! Gosh. Not used that for years. Forgot it existed. For the motion plots i put the equations into python. Cheers
Great work. It shed some light on crank lenghts. Thank you.
@PeakTorque Could You make a follow-up for this video, regarding how one should choose crank lenght?
I'm 189 cm with 91 cm inseam (long limbs, shorter torso). I have both 172,5 mm and 175 mm, i "feel" that I can produce power more easily with shorter ones (even with such minor difference...).
I really enjoyed this years Berkshire Crank Length Review with special guest Warren Buffet. Great watch 🤓
It would be good if you did an analysis of why light bikes feel fast even though the acceleration of the bike plus rider is only 1-2%. I think it is because of the force or impulst which comes back through the seat and handlebars which is due to the lower inertia. I can be bothered working out the maths and I’d probably stuff it up
You start out with hip angle-but you seem not to be emphasizing KNEE angle-and opening that up is a big deal if you have knee pain or a knee injury. I went shorter and it was *way* better. I also moved to more of a midfoot cleat position and that also helped.
Excellent vid. I made one a few years ago trying to debunk the myth of 'longer cranks = more power', but your figures, calcs and schematics make it much clearer!
You have also assumed the footblade as fixed, but you can decide to run the cleats forwards or aft.
I have a problem with your logic of why taller riders don't need longer cranks. It seems obvious to me that if you scale _everything_ up by the same factor all of your angles will be the same, and all of your velocities and accelerations will be proportional (The same if you normalize them to the scale)
If a rider is 10% bigger on a frame that's the same shape, but 10% larger, using cranks that are 10% larger, and the seat height, and reach to the handlebars are 10% larger, all of the angles will be identical. All of the velocities and accellerations will be 10% larger, because the whole system is 10% larger, but your graphs should be identical if scaled appropriately.
Should a long legged rider with longer, often stronger, muscles be limited to a (proportionally) narrower range of motion to produce force through? That doesn't really seem logical to me.
That's not to say, there aren't tall riders who couldn't benefit from shorter cranks if there's other reasons, but if you're going to analyse the linkages, you should at least see that we are already using proportionally "short" cranks at 175mm. Assuming identical proportions, a 165cm tall rider like your friend, on a set of 160mm cranks will have the same angles, and proportional accelerations and velocities to you or I (I'm also 194cm tall) riding 188mm cranks.
Unfortunately, It's difficult and/or expensive to even try it, as the availability of longer cranks is very limited, and the bottom bracket height on most bikes makes it a little iffy too.
Great piece of work, thinking and visually attractive presentation. OK it's a model. There are assumptions. But it's interesting to see what can be derived from that, knowing that it's not a perfect repesentation of reality (yet... :-) ). Curious to see what your real world experiences are with the 165mm cranks. Look forward to a follow-up!
Man, if I had a cyclist/engineering professor back in my Uni days. Dynamics and kinematics classes would have been more interesting.
Bravo - separating fact from fiction! I'm adjusting my seat height and saddle position tomorrow! But I need your torque analysis - please. I'm 65yrs old, 186cm tall, recovering from covid pneumonia a year ago which totally sacked my lung capacity and muscle mass. About 4 months ago I changed my crank length from my traditional 170mm (sometimes 172.5mm) to 175mm crank. I use a hacked drive train (48/38/28t x 11-50t). I’m not a weight weeny by nature, but I have managed to reduce my Surly Straggler down to 21.6 lbs from 28.5 lbs with phat 38c tires. With the longer crank arm, I feel more power and can accelerate faster in shorter periods, and I can keep peddling through varied flats and steeper slopes more often and for longer periods of time. I watch my cadence and it's easier to keep it in the 85/95 PRM range. The biggest plus of all is I get outside and away from a trainer in a room watching a flat screen, which I hate. So far, I've regained about 75 percent of my former strength. My stamina is still the sh*ts though. I would really appreciate your crank length vs torque analysis. I understand what you said about crank length vs gearing, but I'm convinced a longer lever (crank arm) is a benefit across the entire gear range for sport riding vs endurance/road racing.
Very well illustrated, love it someone shows the numbers.
Praxis and Rotor both make 160mm cranks, so does JCOB; You'd need a new BB though for Praxis or Rotor cranks
stunning presentation and analysis
Do you know if 'effective seat tube angle more important than crank length' is still true to the same degree on say a S(52cm) frame rather than L/XL(~58cm)? - In my mind it would be less impactful the smaller the frame, right?
for the accerelation and speed study, did you use a constant bicycle speed or constant crank rotational speed, meaning usually with a shorter crank, omega would go up
Out of the saddle only 172.5's work best for me, leverage must relate to structure, I'm assuming hip width, the mechanical advantage doesn't change.
Ymmv 🍺
Excellent video. Now if we could only get small people bikes designed with lower bbs and smaller wheels as well.
This analysis was awesome. Thanks!
Do you think there would be a model where all the measurements could be plugged in and that would generate the best system? To include seat angle, leg lengths...
Interesting you brought up empirical measurements vs. metric. A colleague mine is doing _his_ research masters in the study of number systems and whether different systems have intrinsic properties that have a benefit in solving particular problems. I don't know his conclusion yet because he hasn't finished but as I see it base 10 has no more significance than most other bases. It's just the number of fingers and thumbs we have. It only has 2 factors while base 12 has 4. The more factors the more numbers can be represented precisely. In that regard base 12 is superior.
Interesting!
Yes, but what _base_ is imperial in? (still base 10, but ignoring that...) 12 inches in a foot, 3 feet in a yard, 1760 yards in a mile.
Yes, our number system is fairly arbitrary being base 10, but there's still something to be said for using exponents of a base unit, rather than arbitrary counts of base units and memorizing a bunch of conversion factors.
did anyone else jump a 2:48 when the audio changed to the back right!?
Great analisys, would you go shorter for road. Do you use 175 on TT as well now?
How does ST angle or more importantly , starting with correct seat angle for geometry of frame and saddle set back and height effect correct crank length , here ?
Very interesting and I agree with it. I have a few questions that you will have better knowledge of and may be able to help.
Does the foot not count as a lever? Surely cleat placement would impact all of these angles?
Would the longer cranks not be more efficient if the body can tolerate them? For example for the bike to travel the same distance, I think you would have to do more revolutions on shorter cranks than longer cranks, therefore more drivetrain resistance and muscles going through more cycles (muscle relaxation affecting contractions ability). Hope this makes sense as I've struggled with optimising crank length. Generally I like shorter.
Alexander Hardy No not really, because you have gears to compensate for that, but you do have a slower foot speed with shorter cranks so can increase your cadence.
Always use shorter crank for giving you better cadence, when in the last kms of a long ride your cadence will drop naturally. Having longer cranks will decrease the cadence even at the beginning... Even mtbiker are switching to shorter cranks. For the cleats lots of bikefitters are moving them back... Triathletes have them at the middle of the foot to reduce calf muscle fatigue for the running session
@@waynosfotos Cadence isn't arbitrary. Equipped gear ratio varies by weight, so it does matter somewhat.
The 'tibia' or shin length of the link is assumed to be the hypotenuse between the actual tibia length and ankle to cleat measurement. This is an approximation to make it work in the four bar analysis.
@@LucaBonato You're talking as if "better" cadence always means faster. I generally ride with quite a high cadence on my 180mm cranks. yes, my cadence dropped a little, but so what? Now I'm spinning 95 instead of 100, but I've got a little more leverage, so I can push a slightly harder gear too.
Hello, what kind of software did you use to draw the pedalling effect ?
So here’s a question if someone was running a large single speed chainring 50T would you run shorter (165-170) arms or longer for less fatigue and better power or larger for more torque?
You are measuring from horozontal not the actual hip and ignored the action hip extensors. The imbalance caused by steep seat tube angles is a problem.
Women swap out their cranks for 160mms? There are few choice at 160mm in crank length. Maybe you meant 165mm.
I've switched to 165 from 170 a few days ago. When doing a steady 8-16mins interval around ftp, the heart rate was 2-4bpm lower than using 170.
And one more thing I noticed that it is easier to push down the pedal stroke because the starting point on 4/5 o'clock position is a bit lower.
Did you change saddle height?
Richard Harding yes, I raise it up about 5mm
Heart rate is affected by lots of external forces, 2-4 bpm could have been anything.
Since Pogacar has dropped down the crank lenght from 172,5 to 170 I think he has lost some power in the climbs. He pedals with more cadence in flats classics and climbs, but years ago like in the final TT when he won the Tour of France to Roglic, he seemed to have less cadence but more power in the climb, in fact he won 2 Tours with 172,5mm cranks. Jonas Vingegaard is running 172,5 and he is even a smaller rider 174 cm, and look how his knees go upper than Pogacar´s knees now. So I think that deppends of your style or riding as Jonas Vingegaars for example likes to have less cadence and going with more strength in comparison for example of Roglic who also goes with 170mm cranks but with a lot of cadence. I am saying that because nowadays it seems shorter cranks are better, but I dont thinks so, it is like a fashions, and it is not for everybody.. it depends of your riding style...
Huh....today I switched from 170 to 175mm and my first long ride just “felt” better. 6’ with ridiculously long legs, platform pedals, and oval chainring. Used to run 180mm, so....😶
You mean 175mm to 170mm?
Imran Hussain - No...170 to 175mm. 170 was just too short for my bike and my legs.
@@ClockworksOfGL I'm 6' 1/2" with 37" inseam and also find 170 too short. 172,5 is ok, that is what I'm most used to. Now I got 177,5 on the road bike and 175 coming to the TT. The experimenting continues...
Glad I'm not the only one. I'm 6'4" also with very long legs for my height. I definitely prefer the 180mm cranks I'm running now to the 175mm I was using before. They feel better on my knees when I'm sprinting, too.
I got 180mm cranks once for my mtb and it was a mistake. 175mm was better.
can you do a video on oval chainrings?
I have difficulty accepting crank length is not effecting torque, this video and others state that you manage that with gearing and cadence. I see two machines working, just like an engine and a gearbox. The engines is making power and gearbox is putting it to the ground, ignoring crank length i fel is like ignoring bore stroke in an engine saying it's all in the transmission 🤔 The transmission is a ratio device who needs power externally
If u would have only one gear, u would have less torque. But with gears u can overcome this by a higher cadians. Maybe a shorter crank length acts somewhat like adding a tooth to the chainring
Worst thing about this video was that it ended! Really informative and thoughtful analysis of something I’m currently trying to get my head around. Thanks 👍
Beautifully done; loved the analysis!
FFT!!! Could you add a video for all us fast-tempo long distance for-fun-pleasure riders. Less so than this video for explosive-power-racing types !!!! I'd love to think I'm fast and unlike Alehandro I was still fast at 40 and now 43 I've lost power and now just enjoy zone 4 no zone 5's
2 key problems I have with this analysis are failure to adjust seat height with crank length and the acceleration analysis assuming consistent velocity.
When crank length is reduced by any measure, if saddle height is adjusted such that the bottom of the pedal stroke remains consistent, the effective change at the top of the pedal stroke is doubled.
Also, there are several studies that show that reducing crank length results in increased preferred cadence. This would mitigate some if not all of the acceleration difference we see in your graphs.
I also suspect that most cyclist's have a preferred/threshold of force per pedal stroke, and this is why we see higher preferred cadence for higher wattage.
I was thinking the same thing regarding the lever x velocity; that the increased cadance to compensate for the shorter arm would mitigate (part of) the acceleration difference. Curious how much it actually is.
Been riding for 30+ years. Always had 170s, am 5' 7", and noticed that I always had trouble accelerating from a dead stop, or ever, as compared to my taller compadres. Switched to 165s about 10 years ago and, man, what difference! Changed everything. And now I know why. Thanks so much for this.
its because when your thigh or femur is slightly lower it will produce way more force compared to get femur being at 90 degrees relative to upper body. Its like doing half deadlifts. Also whenever I watch taller rider their knees never go up the same amount as it does on shorter riders. Not fair.
Fascinating study you’ve done here. I’m very interested in following your progress. My academic background was in Human Factors Engineering and Ergonomics many years ago before I started cycling. I have been searching for an analysis just like yours. I like that you also mentioned leg mass as well. I am about 185 cm tall with large feet (size 47), and big legs. I also have fairly long tibias. I do not use a power meter but I do get the feeling that I cycle better with shorter cranks. The joint angle I am concerned with is the knee. There is a very powerful fulcrum there as well and I want to continue to preserve my 65 year old knees. I haven’t measure power but is seems to me I am able to generate more power at the pedal with the more open knee angle a shorter crank provides. Knee angle and hip angle are related but I haven’t paid attention to hip angle. I look forward to seeing your next video on the subject. Thanks!
Oh man this brings back dynamics and kinematics studies from uni... Love it.
I touched on dynamics at high school, remember fluid dynamics in physics class. I remember we had to calculate the torque and kilowatts required for an oil pump to deliver X amount of litres per hour at a given RPM. The fluid viscosity was set and the pump volume per cycle was also set. Pretty simple with given data much harder to engineer.
As I aged, I noticed that my warm-up for rides to the point where I could accelerate with the group was taking longer and longer. I am 6'4" tall and have used 175 cranks forever. I decided to try 172.5's, and that warm-up period more or less disappeared. Also, my pedal stroke up very steep hills smoothed out. Since I am about to turn 79 (tomorrow) and over the last two years, my power has almost disappeared, so every little bit helps. Over the past 12 months I've ridden 5,000 miles and climbed 80,000 feet which is about one third my normal climbing (last winter destroyed many of the hill roads) I have been unable to easily find the climbs best suited to me. Plus, with my degradation of power, I am too slow to ride with the group and so have to ride solo much of the time. But the improvement in power with the shorter cranks. I am able to continue even on the worst sections, though I am crawling over the steep sections.
Watched this video and would like to comment on your CAD model/dynamic simulation. In that model the angle between your ankle and lower leg is held constant, which you do mention at approximately 12:25. For your CAD model what you should do is constrain the angle of the foot to the ground, not to the lower leg. If you watch riders from a side view you will see that through a full pedal rotation, the foot is held at 20-30 degrees to the road surface. This varies throughout the stroke, and if you could model this correctly in your CAD skeleton, you would see different results in hip angle especially at the top of the stroke (330°-60°). See if you can find videos of experienced cyclists on trainers from a side view and you will see what I mean.
5' 7" (30" inseam) and I find 170mm cranks too long. I've been experimenting with shorter kids bike cranks, 152mm to 130mm, and find that 1mm ends up equaling about 1RPM of perceived cadence. (85RPM @170mm feels like 103RPM @152mm)
The cadence where I can hold my FTP at the lowest heart rate is about 95RPM. That seems to line up with the dynamic model that I should probably use 160mm cranks. Too bad they're such a PIA to find.
Very interesting experiments. Good to see someone trying the extremes. Cheers
@@PeakTorque I managed to get some 160mm 105 Cranks. Instantly increased my average cadence by 8 rpm. Power is down a little because I'm not conditioned to the faster cadence. (Fast twitch fibers in the quads are on fire). Way more comfort, and simpler to find a good fit.
It is a downright shame how many females don't come in metric.
Who wants a fraction of a girlfriend?
Too many imperial women out there?
@@shibaburn7725 Way too many "Imperial women." It is the pathology of Disney and feminism telling little girls that they are princesses.
@@PeakTorque Sometimes, a fraction of a girlfriend is enough... Rgr
ALL women come in metric ....
Good analysis. I ride long cranks (old school 185 and 180mm). Recently I have a bike with shorter (175mm) cranks. The feeling is very different. My second ride with the bike resulted in "exploded" legs after 75km. You really need to adjust to it timing wise. My cadence did not change (94rpm average). In several studies they changed crank length and tested in a short period of time. That would never give a good result.
Looking at oval chainrings in conjunction with this analysis would also be quite interesting.
Looking forward to this as well
The time spent reading or watching how to improve my performance normally yields a negative return on investment vs spending the time actually training. This video is an exception. It inspires informed experimentation which may indeed uncover flaws in my current setup. Being able to present significant ME theory to the point of almost sounding sexy is quite a testament to your overall skill set. 😊
I would love to see how an oval chainring plays into this equation and also the other interest would be how cadence speed would it should change to create the same output. Great clip.
By surveying some decent bike fitters… that fore aft seat position should not be used to open hip angle because moving seat forward means your torso can become unbalanced as it is more cantilevered over the bars.. this results in saddle sores and numb hands.. therefor fore aft position should be driven by balancing upper body weight.. I’ve experimented with this (and reach.. discovered that handlebar width increases reach!) and my numb hands and saddle sores are GONE!!
Much better to use crank length since it doesn’t throw off everything else.
Noice! Have you considered or already done the 5 linkage version, adding in the ankle-to-cleat link? The whole "cleat under ball of foot" rule of thumb has also been subjected to actually doing the science and thinking about it from a biomechanical POV, with cleats being closer to the midfoot showing some real benefits, such as increased foot stability and reduced calf loads/fatigue.
I'm 69 years old, 180 cm tall. I have 2.5 cm longer legs and shorter torso than average for a male of my height. Usually ridden 172.5 mm as that's what the bikes came with. But my Specialized Steel Langster had shorter cranks (165mm?) and I absolutely loved it, rode it very hard up and down hills in traffic and in rural areas. I had a chance to get shorter cranks when my 2018 Ultegra cranks were recalled and replaced last year... but I forgot! Now about £250 to get shorter cranks and that is a long way my pension budget list of desirable items
"in a 5 hour live stream about crank length" hahahaha
Very interesting. One idea I’ve got about the limitations of short cranks is that you spend less time in the down stroke of the pedal (due to shorter range and higher RPM). This gives less time for RFD (rate of force development). RFD is basically how quickly and simultaneously your neuromuscular system can recruit high threshold motor units. To demonstrate this, flick your hand with your finger. Supporting the finger at the nail with your thumb gives time for RFD. If you try flick by just extending the finger un supported, you can’t generate as much force.
Secondly, overly long cranks would put you out of the range of motion where you have maximum Actin and myosin cross bridging. This would also limit your force production. Example, flex your wrist (bringing palm towards your forearm) and then try to clench your fist. You have less strength than wrist in a neutral position because you’ve pre shortened the muscle and put it out of the range of maximal cross bridges
Exactly right with RFD. I think i mentioned that somewhere short may limit that window for torque deployment for bigger riders.
Thanks for the comments btw. I'm no expert on biomechanics/biology.
So would shorter cranks be better as your legs would be closer to resting neutral position? I think of long cranks as having to do a deeper squat. I could squat way more weight if I didn't have to go down as far.
Alexander Hardy yeah, if you had unlimited time to generate force you can achieve the maximum force in a narrow range of Motion (like the top of a squat). But, because the pedal stroke is high velocity, a shorter range of motion reduces the time you have available to generate force (it takes time for your CNS to send the signals and activate all your motor units). Realistically though, I don’t know how much difference it makes between 165mm crank and 170. I think track riders tend to use shorter cranks and they achieve very high peak power output? However, they are very explosive athletes and do a lot of weight training so they would be very good at quickly generating high forces. It’s possible that as you decrease your explosive strength deficit (the difference between your maximum force to the max force you can generate in the time limits of a particular movement), shorter cranks would become more useful to you? If you have low RFD maybe you need a Lower cadence and longer pedal stroke? Sorry not very helpful there, just thinking out loud.
Very good, and yes people have many myths surrounding shorter cranks, but there is more;
Shorter cranks require a higher seat position, this may be desirable for a person using aerobars to get the back flatter
Shorter cranks means a slower foot speed, therefore you can increase your cadence easily, this may also be advantageous
For track, 165mm is used for clearance, but they run many different fixed gears, so does it make that much of a difference?
Your power remains the same as as you said, you have gears to compensate for the torque advantage at the crank, the whole action needs to be considered.
Some proclaim shorter cranks are always better, but there is disagreement in the industry.
It is clear that you need to study a number of factors as to what you are trying to achieve before making an adjustment.
A “general” statement, (if there is such a thing relating to cranks) if using aerobars a shorter crank can be advantageous, for road riding it isn’t so important
This is way too simple. You need to consider ankle movement.
at 5'7" with a 29" inseam i find the 165 cranks on a medium frame work for me because my upper body is long so i need to stretch out but the little engine needs those short cranks to spin well. i notice a huge difference between 165 and 172.5
here's the worst... when i was asking about this at a local bike shop ( B.S. shop more like it ) i was told in a dismissive tone ( 172.5 is standard. Same thing when i queried bar width. I didn't even buy my bike there!! Then again, it's Toronto where all shop owners have the attitude of they do not need your shitty money.
165 made the difference for me and I don't even know the math as well as you. I just feel it.
I went for 220mm cranks, from 200 originally then 215mm, reason being, for me they feel comfortable. Like having a nice stretch or walking with a longer stride. I do have a 39 inch inside leg length though.
they've found bones of your ancestors, according to late night History Channel
Great video, very informative and I love the use of engineering to debunk cycling myths.
Did you ever make the follow up video about force? I couldn't see it
“Can’t be arsed to convert imperial to metric” ....
I have a question regarding the the change to crank arm length: Why did you not change the seat height by the same amount?
It is recommended to change the seat height by the same amount you change the crank length to reach the same effective seat height again. I see the value of isolating a variable in analysis, but in this case it does not seem correct to isolate this change when you will always change seat height at the same time. Further more so as in the next step you talked about the benefit of raising the saddle and setting it further forward. This would be the next logical step after reducing crank length anyway. Seeing bikefit as a system, where one parameter changes others at the same time, it seems to me, that it is not advisable to isolate changes for analysis.
Great analysis. I think the main problem is that road bikes are still way too conservative on their geometry. Crank length is one point - but the much larger problem is that road bikes seem archaic when it comes to findings on what is faster on mountainbikes, think Mondraker Forward Geometry or Pole bikes - mow more or less implemented in all bikes. Ideally we want much steeper seat tubes - maybe 76-77°, maybe even 78° as on Pole bikes (though then the more you use your bike for climbing - the steeper you like your seat angle), longer reach but shorter stems, and much slacker head angles (and yeah wheel base will rocket from the paltry 99cm to 110-115cm or so - notice enduro mountainbikes have arrived at 130cm already for a size large). The main problem is the handlebar width - going 10-20cm wider would likely be really beneficial fore most going uphill, but really inefficient in the wind. This would resolve a lot of too much weight on hands/shoulders problems. Someone really needs to think forward, forget UCI norms, and look at things that made mountainbikes fast. Then get people to train on a new geometry for some months and compare speed and comfort. Some things from the mountainbike side may not work on roadbikes (for sure no 75-80cm wide handlebars) but a lot will. To counter the slacker head angle and weight distribution - the chainstay length will need to grow too - however road bikes likely need much less weight on the front wheel vs mountainbikes - so shorter CS = less weight on your arms = more comfortable. And yeah if crankarms reduce in size, the long needed evolution of chainring sizes going smaller needs to continue too. Average Joes tend to run way too big rings up front instead of spinning faster and trying to choose a small ring that allows them never to drop below 80RPM on their steepest common climbs.
It's crazy how conservate and stupid a lot of the bikefitting is on roadbikes - trying to fit people onto frame geometries that are simply wrong from the start. And yeah it needs a radical departure from the status quo. Most of bike fitting is simply an reaction to wrong bike geometries.
Agree, frame geometry needs to be looked at, seat tube angles are far too relaxed. I've always thought we should be far more over the BB in order to sync the lower body. I always slam my seat as fwd as I can and never have pain
I went from 170mm cranks down to 165mm in an effort to improve pedal stroke smoothness when in the aero tuck position. Now I know why it works!
Floydie I did the same! I even feel more confortable breathing while riding on the drops.
I also went from 170 to 165 at 5’8”. It made a world of difference, The typical crank lengths are wrong.
When I was racing off road in the 90s, everyone was using 175+mm cranks, but being under 5.5 ft tall with short legs, I found 175 cranks just too long. I switched to 170s and never looked back.
Id like to see you do a force vs. Femur/Tibia angle at the pedals. That coupled with the crank length should give you the best idea of optimal crank length to run.
Love the analysis, but (I think you know) its not a 4 bar link...its a 5 bar link. I know you’ve intentionally made the ankle fixed in your model, but If you are ignoring the range of motion from the ankle then you are missing a key attribute. If (as in your CAD model) the foot to shin angle is static then from my analysis of many riders, they are wasting significant range of motion and not engaging the power of the calf/shin muscles in the power stroke. In my own tests, and tests with many customers, I can produce 20% more power through effective “ankling”. So I’d suggest the model needs updating, as Ankling does have significant impact on correct saddle height, power phasing, muscle load etc. which I believe will have impact on your analysis. Obviously foot length and cleat position will then make this more complicated ;-)
I'm one year late, but this is a truly fascinating comment - the 20% more power through effective "ankling" is an impressive number and I would love to get at least a rough idea of what this involves - some level of toe pointing to involve the calve muscles at the lower part of the stroke I presume but then perhaps heel dropping at the top too?
I went just recently over to 165mm cracks from 175mm cranks that I have used pretty much all my grown life. Well in the first two weeks if felt like the smaller circle you are pedaling in was so restrictive that I was about to change back. You got no power, and it feels like you are on a those tricycles if you remember those from your early childhood. But I noticed that I never ever had any pains or similar issues in the knees and the like, and even though I still am lacking in power it seems I am adapting to this as well. Oh yeah, I am 172 or 5,6 or 5,7 or something like that.
I'm running 155 rotor cranks at 6 ft 3 they are great for running of the bike. Maybe losing a little force but over longer tri distances the less stress on the hip flexers out way the trade in my opinion
wow
That bigger riders need longer cranks is not a fallacy, but what it does not do is qualify the starting crank length.
A longer crank just means the more you have to pick your leg up to get a full rotation, so being longer in the legs doesn't really make that advantageous. It's like saying larger mtb riders should be on bigger wheels. Not true at all, merely that smaller riders can't always get the ideal geometry to fit around a larger wheelset. A large frame can have any size wheel it wants, a larger rider can have any size crank they want. I think the same goes for crank length.
@@Metal-Possum why don't we all just switch to 100mm cranks, and spin away at 180RPM on the little ring?
If you run 160mm, you're just having to lift your legs higher.
nwimpney I know you mean this in an absurd way, but I think you’re onto something. 180rpm is hard for most people to sustain, regardless of crank length, because of the frequency at which muscles need to fire and relax. So the biomechanically ideal crank length (besides positional stuff) would probably be the one where the rider’s preferred foot speed and the rider’s preferred firing frequency meet. I’m not sure how you would determine either one, though.
Interesting. Never thought about it in terms of degrees/s of the femur.
I have 175's and am considering 170's for less hip angle. But at age 60, I am more concerned about how raising the seat will then impact saddle to stem height and the changes I may have to make to the front end.
One thing leads to another...... 😁😁
in my experience, it is all a matrix of bike geometry, body and adaption, and cycling environment ( eg. hilly, flats, urban, short circuits vs. endurance) - in other words, numbers (175, 170) are meaningless.
Shorter is easier on the body. ‘MOre comfy
Thank you for this content man. This is exactly the thing I've been looking for. Keep it up!! Definitely looking forward to more analysis like this.
I'm 5'6 / 165cm with 29" inseam. I modified by machining two new positions on Shimano arms from 172.5 to 155mm. I also lifted my seat by about 15mm.
The difference was compelling. For me, MUCH smoother and I stopped rocking on my seat. My Zwift output appears to have gained 5-10w at same heart rate.
Too many geometry factors here for me to consider (or understand). My 'seat of the pants' mods tell me I'm OK with the new geometry.
Fantastic analysis, thank you for posting this.
Really enjoyed this, cracking explanation. Solidly de-mistifying bike fitting. Subscribed!
Just by curiosity, have you taken into account the muscles that are engaged given the crank length? I reckon it might have some effect on power. Like muscles might flex just a bit more to get more juice out, or some crazy shit like that. Just a thought
Best quantitative explanation I have come across. My background is on robotics and controls. I’ve analyzed the Puma (swing, shoulder, elbow, spherical wrist) geometries “many years ago”. I have not come across a proper linkage/geometric analysis like you did here. Thanks for creating intelligent, analytical content!
Subjective comment: I’m 5’9” / 175 cm and in my late 50’s. I live on a small mountain range where my climbs average 5 to 9% with gradients of 14 to 18% common. I’ve had several road bikes in size 56 cm and they all came with 172.5 mm cranks. After reading and watching about crank length I went with 170 mm on my last bike purchase. I couldn’t be happier. The difference when climbing was immediately noticeable. I wasn’t straining as much, but I was spinning faster. My times going up remained about the same, but I feel better at the top. Thanks for the informative video.
Hi James I've always thought getting the right riding position is an art, but the science is all new to me. I would have immediately guessed that a longer lever / crank would make spinning easier, but I suppose that's where ergonomics comes in! Found your comment very interesting 👍🏾
Thanks,I shall follow with interest. Another aspect: what if you have different leg length's and/or variances in tibea/ femur? E.G: my right femur is 22 mm longer than left,while the right tibea is shorter. Overall my right leg is 37mm shorter. To complicate matters my right ankle has a fusion and alignment issues,making for complicated bio-mechanics.
Real world experience; Male, 177/2.5mm v 165mm height, height;177, long femur (52/48ratio, women legs). 45 years of riding and racing.
Longer cranks are more fatiguing, as most long rides have long spells of 160 watt output, just spinning. So small circles are less fatiguing and more efficient due to the flattening of the curve (as shown). I discovered this years ago and my climbing improved ( 1hour plus road mountain climbs) again less chance of peddling in squares and using gears...Also moved saddle forward, more 130mm stem for stable mountain descending (which I love, completely changed the handling for the better), which again helped climbing in a smooth manner, revs the standard 75-80rpm (very few can rev at 90 efficiently and blow).
This all came form that original ironman triathlete paper concerning 140mm cranks as an extreme, about 10 years ago..
Conclusion; less fatigue, better run off the bike, faster time.