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- เผยแพร่เมื่อ 7 ก.ค. 2024
- In this video, I use the data acquisition system and software suite I've built out to quantitatively analyze traction in the field. I compare an old rear tire with a brand new one. Shocker, the new tire is better. But what does better actually mean? This is what I seek to answer with this research project
![[LIVE] : ONE ลุมพินี 69 | คู่เอก "กุหลาบดำ vs นาบิล"](http://i.ytimg.com/vi/PNM6U8e_HMo/mqdefault.jpg)
That old tire has EXO casing and survived this long??? You are super lucky
Super cool video! Thanks for all your analysis and thoughts.
I would love to see the overall times of the runs you did with old / new tire.
Thanks for doing this experiment, very insightful! Some elements I’d love to see included if you were to take it further:
1. More data on varied trails and conditions. Curious if you’d get a better p-value on slick black tech vs blue flow for example.
2. Blind the rider to which tire is being ridden. Placebo alone can easily produce the kind of p-values you measured. I think it has a huge effect with anything related to feel like this.
3. Try with other riders, do different people get different benefit?
4. Normalize the data by speed and/or acceleration to minimize differences in how each run was ridden
Great ideas. Thanks! I'm resource/time limited which is why I didn't do much of what you mentioned! But yes, multiple riders, blind studies, and just a larger dataset in general would be huge.
What I will do sooner or later is what you mention in 4. I think that normalizing based on speed will be an interesting thing to look into, especially because it will give insight into how, on average, one rides differently to compensate for a worn down tire.
Cheers!
Steep tech climbing is where I notice the difference the most. Especially as we enter the fall/moist/leaves season... just gets frustrating and end up having to push through too many sections because the traction just isn't there. Also when my rear gets bad, in fast hard cornering, it sometimes wants to become my front tire, haha.
There is an issue when comparing front and rear tires speed for measuring slippage:
the rear tire always goes slower than the front, even with no slippage at all. Because each time you are steering, the front tire is rolling more distance than the rear. And you are always steering, that's a big part of what makes the bike stands on its wheels.
Correcting the formula by a function of the steering angle should add significance to the datas.
Good catch! I have a simple way of accounting for this by setting a slip threshold, only counting times where the rear wheel is below set percentage= of front wheel speed. This allows for false positives to not rack up, while still catching perceptible wheelslip events. I determined this experimentally by riding with a feedback button and hitting it for all traction loss events I felt, then tuning the percentage to pick up on all those. This is partially explained around 4:06, but I'll do a better job of it in my next video. Thanks!
While your p-values are not impressive, we have to appreciate that you calculated them at all. Seeing the same thing done for every "bike test" out there that includes timed runs, would probably be quite an eye opener to the value of these tests. Or lack thereof.
It would be great if you had done a lot more testing with this, but I understand not wanting to put the old tire back on. Also you'd probably have to replace the new tire a few times for a prolonged test to keep it "new"
For the rear wheel it's usually the side knobs getting eaten on the inside bottom so they get flayed out. On MaxxTerra Dissector that is about 1000km that they are clearly worn and can be turned over.
I found this changed as I progressed as a rider. Initially, when my skill level was low and I did not ride aggressively (except to push myself from a cardio perspective), my middle knobs wore out soonest. Now that I ride more aggressively, specially in the turns, my side knobs wear out (start turning over or ripping right off) before the middle knobs wear down.
And I also found out if you run your tire pressure too low it's your sidewalls that will wear out first.
This was so much more rigorous than I expected!
:)
Yes, specially in the algorithm development to weed out false positives.
Great video! Everyone can see what a new tire is, but probably have very different opinions on what a worn out tire is. Must have been bad for the buddy gift, but I'd love to see it.
I think a more relevant measurement from a performance standpoint would involve threshold braking:
en.wikipedia.org/wiki/Threshold_braking
"Braking beyond the slipping point causes the tire to slide and the frictional adhesion between the tire and driving surface is reduced. The aim of threshold braking is to keep the amount of tire slip at the optimal amount, the value that produces the maximum frictional, and thus braking force. When wheels are slipping significantly (kinetic friction), the amount of friction available for braking is typically substantially less than when the wheels are not slipping (static friction), thereby reducing the braking force and eliminating steering ability. Peak friction occurs between the static and dynamic endpoints, and this is the point that threshold braking tries to maintain.[2]"
You are correct. You're probably familiar of what brake force looks like when plotted against time as force ramps up, get to threshold (max brake force), and enter slip zone (drop in brake force) (see page 38 here: books.google.com/books?id=rJTQxITnkbgC&printsec=copyright#v=onepage&q&f=false). In the past I have used strain gauges at the brake mount to get force, but since I don't have access to those resources now, I am using slip as a proxy. When the rear wheel starts to slip, presumably, we have moved past the threshold braking point (highest force attained on the curve), and so the slip measurement is kind of a poor-man's way to do what a strain gauge would do better. Does that make sense? Thanks for the insight!
Good stuff mate
Cheers brother!
Nice work! This is cool to see. Have you looked at measuring friction coefficient vs slip ratio? Viscoelastic materials like rubber can have peak friction when there is a small amount of slip, which could give some more insights to the results you've got so far
I feel like you focused on measuring the wrong thing - slippage of the rear tire going downhill. I feel the knobs on your rear wheel are most important for traction as you pedal (that's when you don't want wheel slip at all). Going downhill, most of the hard braking happens on the front wheel - some slippage on the back wheel doesn't matter too much going straight. Where it seemed you felt it affecting your ride was on steep turns in the chute where the side tread being bald would affect control as the tire slips. The tire was still locking up with the new one, but it wasn't sliding side to side as much, giving you more control and giving you a better ride feel. With this better control you probably unwittingly eased off the brakes more often, regaining rear wheel rotation sooner in those sections.
For measuring braking ability on new tires vs old, I think a brake to stop measurement would be better to see which tire lets you decelerate in less time/distance.
Cool stuff nevertheless. It's fun seeing that kind of data and testing, as it makes us really think about what is happening when we hurl ourselves down mountains on our expensive two wheel contraptions.
I wonder if datalogging the temperature of the brake calipers and brake travel would make for an interesting test. Maybe you could quantify brake fade and see if theres a tangible difference between say shimano brake fluid and Trickstuff Bionol (the latter has a higher boiling point)
I think the findings are interesting since length of time in slip event affects control evelop of the bike. That is, since we're accelerating due to gravity, the longer we spend time in slip the more speed we have accumulated at the end of the event. The more speed we accumulate, the more control input is needed from the rider.
nice! Would be nice to get a closer visual look of the old tire vs the new one. great test!
Different models so he didn't show them
when u break in off road conditions slipping is sometimes positive also in off road conditions maximum breaking power is when wheels are locked (sliping)
I'd be interested to see a comparison of the stopping distances.
Very interesting test.
I think the traction is one thing, and grip is another.
So how easily, how much, how long does the rear wheel move more quickly than the bike speed under pedalling (wheel spin).
And then your test, of what happens when the wheel slides under braking.
I'd also wonder about the peak values, things hide in averages as someone once told me.
Well done, and fascinating to watch.
It’s been 10+ years since my last stats class so take this comment with a grain of salt, but I think if you combined the two probabilities (time spent slipping AND magnitude of slippage) you would find that the results are much closer to statistically significant
did you measure the tread height differences? curious how worn the older tire is. thanks btw
Matt! Nice video. Did you ever get to use that speed sensor disc with tons of magnets from the Mahle X20 system? And/or are you satisfied with the resolution from 6 magnets?
Hey Mike! I did not. For the purposes of this study, 6 magnets gives more or less enough resolution for what I'm looking at. But I really would like more. There are some fancy things out there allowing for something like 100+ pulses per rev which would be sweet.
I think higher resolution would be especially useful for correlating with data like braking force (from brake hose pressure or from strain gauge at caliper).
Cool video. Did you use both front and rear brakes in the test? I would think just using rear will have a huge difference in the slip percentages you were seeing.
What were your sector times like comparing old vs new? It looked like your new tire speeds were quite a bit higher than with old tire. Sometimes for the data to make sense you have to be comparing the right variable.
Will! Good to hear from you. Total run times were basically the same, but the run-level times are less important to me as the specific sections I was interested in (which you allude to with "sector times"). For the chute, believe it or not, my speed (from the first tree at 6:57 to the tree at 7:08) was almost exactly the same between tires across all runs. About 11 seconds. You can even do the hand-wavy math in the video for one of the bald tire runs (7:09 to 7:20). I can compute this accurately on my end by using GoPro + logger data synced.
What I want to look into more is binning traction loss events into bike speed bins. Which I think will give some insight into the different ways we ride to compensate for a bald tire, and just ride characteristic differences in general. You're totally right, pinning down what we actually should be looking at is central. I'm not convinced I've totally found what that is yet here, but I'm on the right track.
Sector time is kind of an all encompassing measure. But that might be the end goal with different equipment, right? If it gives you more control or confidence, you should go faster. Braking power (m*a*v) might be another measure you could compare.
I applaud your efforts, but you've compared a worn out Maxxis to a new Schwalbe...
...or Specialized.
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