What Fork Offset is Best? Steering Geometry 101
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- เผยแพร่เมื่อ 31 ก.ค. 2024
- A deep dive into the basics of bicycle steering geometry.
This topic has been relevant in my world recently, as I have some decisions to make for my next bike. So I figured now was the time to put a video together explaining how all of these things work together, and some of the common misconceptions to watch out for.
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The only video about fork offset that actually does make sense. Thank you.
this video gives 3 kicks in the ass to those GMBN offset videos
Stating how offset increases affect wheel flop is excellent. I was originally thinking more offset, increasing wheelbase, would add stability and increase straight tracking. I've got a 70deg HT angle, and a Fox 34 Stepcast and trying to switch to a carbon fork. The Enve fork can switch from 44 to 52mm offset, the Whisky fork is fixed 51mm offset. Plus, the Enve fork is 10mm shorter in length than the Whisky.
Спасибо братан, я собираюсь покупать новую вилку и хотел бы сделать управление более резким, думал что чем меньше рейк тем резче управление, а оказывается наоборот. Спасибо еще раз!
So so glad I stumbled upon this video... I need more.. I have been wanting to increase fork travel but know that is going to change the geo on my bike and have been looking for ways to offset the change in fork length so it doesn't affect the climbing ability and to a lesser degree, the handling. I will probably have to watch this again to understand it even better but a video including stem length, and perhaps bar sweep and height and other variables included would be so helpful.
Best Video to offset I've found👌
Excellent way to visualise steering mechanics! Thanks!
Beautifully explained!
Thanks for the very informative tutorial. I would add that I use longer offset to give me greater clearance for my size 14 feet.
great info and great explanation.
That was the Best explanation of Offset I've seen in quite some time Brother, and I really appreciate it. I did feel as though I was back in School on this one, again Great Information........🤝🏾🇺🇸💪🏾
This is great information! Thank you
This video helped a lot. Thank you.
Very detailed explanation. In addition to being a mountain biker, i build chopper custom bicycles. And that's where rake and trail angles get VEY interesting! Quite a juggling act if one wants a radically long-forked and raked out bike to be safe and stable. Thanks for the video.
A vertical stem is actually best, with zero flop.
Mike Burrows put together a bike that was fully adjustable to check this. Interestingly BMW have done the same.
Of course then the handlebars are out of reach, so you need a remote linkage. Historically the reason why we have inclined stems is to get the bars close to the rider. A Penny farthing has a vertical stem.
Great video and explanation
Excellent explanation, but needs more detail on riding characteristics for different purpose bikes. Another issue l have with my big feet is foot wheel overlap on road race style bikes.
Thank you!!!
Sorry for my poor English. The current Chisel frame is, as you know, more progressive than the previous one. The factory head angle is 68 degrees and the fork offset is 42mm. Many people modify these bikes by installing, among others, a Reba with a 51mm offset, which significantly reduces the trail but slightly increases the wheel base. The bike will probably be more controllable, but won't there be an effect of a steeper head tube on descents, won't this Reba ruin the gains of the new geometry? By transferring the effect of the change in offset and wheel base to the head angle - will it be a change of about 1 degree or rather a less noticeable value?
the flop is a major characteristic in motorcycle handling at low speed, in rough terrain, the handlebar get stuck or almost impossible to move if you stall the engine.
that's why I really liked my 72* head tube angle on my XC MTB back in 2017.. 2018. that angle was just almost perfect. of course.. for cross country bikes. for enduro or trail it's usually 68.. 67 66* for head tube angle.
enduro is more like 64, 63 now and my trail bike is 65.. lol... They keep making things slacker and slacker. I wanna find that perfect mix of a great climber but also a great descender... My Norco Fluid FS 1 is really close but only has 140mm of fork travel and I would like something like 160mm.
@@snowman22ism true I'm not in Enduro. No trails or hills in my flat area in middle Poland. But yeah 64 in Enduro is more like a standard nowadays. XC is going a bit too crazy with 67 in my personal opinion.
If your bike is too slack, you can now get angled headsets, that change the bikes head tube angle.
Amazing video that clarified many things for me. I do have some further questions though.
1. Why is too much trail combatted by adding an offset instead of reducing the headtube angle?
2.Will you make a video on the whipple model of the bicycle, or any model that attempts to mathematically determine the motion and stability of a bike using classical physics?
Thanks for your time.
Great Video
I don't hit double gaps and ride mostly in terrain with techy climbs and short steep descents. I ride a 2013 Stumpy 29" with a 51 mm offset. It is a great climber and has very precise steering with a 10mm rise 720mm bars. It never feels unstable on gnarley downhills, but I am not on extended ones, like in serious mountains. That would be the only reason I could think to switch to a longer, slacker bike.
good job thanks :)
The flop force is surely the whole weight resting on the wheel, not just the weight of the wheel above the axis?
Great video. I’m looking at a replacement fork but can only seem to get 44mm offset however I’m currently on a 37mm fork. As an average rider, will I notice much difference? Thanks
Well, despite of all the numbers and their affect in rear world, anyone can choose between different offset forks considering the market value too. I'm representing people that don't notice differences between those two offsets. 51mm isn't in "fashion" so you can have a great fork at a discount price. But probably it will be more difficult to sell It afterwards. Give and take.
I agree. Low offset is all the rage these days.
Although, I've been wanting to do an update to this video to share some more thoughts. But the short version is that differences in mechanical trail are subtle. Many riders (myself included) won't notice a difference. The big thing is the reduction in flop height though. I find that to be very noticeable.
I'll always take a higher offset when I can get it.
what effect would have offset of the fork to the head axis
Will a 51 offset give the bike a longer wheelbase. I'm building a bike and I want a longer wheelbase
Great video, best explanation and only one that mentions flop. So what about weight distribution from offset? Does it make much if any difference? Shorter offset gets front wheel closer to rider putting more weight on the front wheel. Changing center of gravity slightly forward and gives a little more traction up front. Guess it is kinda like stem length not just changes reach but longer one puts more weight on the front tire.
The differences of weight distribution, wheelbase, front-center and all that are going to be very minor when talking about the fork offset differences. It just doesn't really move the front wheel around that much when compared to everything else.
As an example, lets say we go from a 51mm offset, to a 42mm. That's a difference of 9mm. With the head angle of the bike in this video, that means we move the front tire horizontally by only about 8mm. Over a wheelbase of around 1200mm, that's a pretty small change overall. But the changes to the steering geometry and such are much more pronounced.
But also for mountain bikes, we typically want to do the opposite of bringing the center of gravity forward. That's why bikes are getting longer and longer, slacker head angles, etc. Increasing the front-center of the bike has many more positive stability benefits off-road than the slightly increased traction of a forward CG.
@@shieldmaidenbikes771 Thanks for your interesting video. Reducing the offset from 51 to 42 doesn't help carry the weight forward, so it improves stability? Traction is more related to the "trail", if I understand. I'm in doubt whether to switch to an offse 42 fork from a 51 on a bike with 65 ° steering .... I don't understand if a variation like this would lead to big differences on the steep and technical.
Great video, but one question:
the way I understand, offset is taking place at the front hub.
With some forks (fox 36 e.g.) you can get different uppers with different rake values (44 and 5xmm if I am not mistaken) so let's say I increase my rake by 10mm would that have the same affect as increasing my offset by 10mm?
Thanks a lot regards, markus
Rake is a different term altogether, and I suspect you are using it incorrectly. It is typically used in place of head angle for motorcycles. For example, a 70 degree head angle is the same thing as 30 degree rake. Just measuring the same angle from the other side, in other words.
But to answer your question, it sounds like you are using the terms interchangeably, so the answer would be yes, it is the same.
At higher speeds, it's the gyroscopic effect that takes over increasing stability. You say here it is the castor and I disagree. I do like how you are showing trail as square to the head bearing angle.
Thanks for the video. I'm a roadie but I'm looking at changing a fork out. So was interested in the theory. Quick question, for the trail calculation on your spreadsheet, is it formula the 'mechanical trail' or horizontal trail on the ground? Thanks again.
It's the mechanical trail. i.e, measured perpendicular to the steering axis.
It would be good to calculate a stability factor and add it to the spreadsheet. And for a fun exercise, find out what is the inherently most, and least stable positions of the steering geometry.
That's something that is in the works. It gets complicated though when you start to figure the effect the contact patch size has. That's something I'll likely get into in a future video!
So what geometry are you going with on your custom build? Are you going to try to minimize flop?
Yes! Minimizing flop is definitely my goal.
In fact, with my current bike I've been playing around with a few factors to really dial in things. It's on my video to-do list to talk about all of that.
I've also been working on making a follow-up to this video. Learned quite a bit since I made this one. But the short version is minimizing flop is much more important than maximizing the trail number.
My bike have 51 mm offset fork its really hard to handle specially on technical trails
Is there an optimum trail & flop? I have an early Levo that I have converted to a mullet, I am looking to replace my fork. My bike came with a 51mm offset fork and I am having a hard time finding the fork I want that comes in 51 (most are 44). I am concerned that I have already slackened head angle with 29er on front, I am also wanting to upgrade to a longer travel fork (150 to 170). Is there a way I can figure the head angle with the longer travel fork? The more I learn about bike geometry the more I feel like I might be making my handling worse.
You can calculate the change in head angle with a little trigonometry. You will just have to know the wheelbase, existing head angle, and then the old & new fork dimensions. If you can draw it up it CAD it makes it very easy. That's usually what I do.
But I would also agree, mullet-ing a bike and THEN adding a longer fork is going to change basically all of the geometry of the bike.
I wonder what's the best offset for my Marin San Quintin 1. It has a 65 headtube angle with 47mm fork offset atm. Will 51mm offset be okay?
51mm offset will be fine. The differences will ultimately be pretty subtle. It really just depends on how 'sensitive' you are to changes like that (a lot of riders will never really be able to tell the difference) and of course what you're looking for in the bike.
If I had to guess, you're probably just using the bike for general 'trail' riding, and not just all-out smashing the rough stuff. 51mm offset is what I would run in that case.
@@shieldmaidenbikes771 you're probably right Mate, thanks for the detailed information. Very much appreciated. 👍
Tried diff offsets . Diff fork lengths... they are all the same. Either didn't notice any difference or anything I didn't get use to after 100 meters of trail..and then it was back to business.
Can we assume longer offset would essentially make the wheelbase "shorter" since it makes it more twitchy
It does make the wheelbase shorter. Technically...
But the difference to the wheelbase / front-center is almost negligible with everything else going on.
As an example, going from a 44mm offset to a 51mm is a difference of 7mm.
When you factor the head angle in, that number gets even smaller.
That's only a percent or two of change to the wheelbase. But the changes to the steering 'handling' and feel are much greater. (and worth it in most cases)
I've been playing around with some stuff lately and would like to expand on this video. There's a lot more going on with the bike as a whole! But I tried to keep this video limited to just the steering aspects.
That video(s) should hopefully be soon!
Actually, now that I think of it, putting a longer offset fork on an existing bike will make the wheelbase longer. Got it mixed up in my head.
But yeah, the changes to the wheelbase are very small.
Can’t have high trail and low flop simultaneously
I have watched how rider's fall over a simple flop , and lost there Handel's..
It seems that the middle ground is the best. Like the 27.5 wheel gives you the best of the 26 wheel and the 29er. And as you said in this video just 26 is better for some types of things as well the 29er. A-10 vs F22 You buy what you need it to do. Thank you for your time and effort in making this video. 💯🇺🇲👍🚲🦺🧰🔧🪒⚙
The wheel size is a variable when calculating the Trail and Flop numbers, but it's important to note the trail and flop are what really give the steering and handling characteristics. Not the wheel size.
In other words, if had a 29" bike, and a 26" bike with identical trail & flop numbers, they would handle very similarly. So similar that most riders may not even notice.