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Just to add something concrete here: shorter chainstays means more movement at the handlebars is converted into less movement of the rear axle. Given two bikes with the same FC, the one with the shorter RC will give the bars more leverage when bunnyhopping, pumping, jumping, etc. The weight on the pedals is constant for a given rider, but you can generate more force.
Wanted to provide an actual link for those interested. Haha
https://forums.tetongravity.com/home/forum/gear-buy-sell/tech-talk/11666848-do-you-measure-ski-tip-and-tail-and-should-we-care
That's pretty funny. The whole discussion is completely meaningless without camber/rocker/sidecut/stiffness/width/area being taken into account. Almost as meaningless as this thread i suppose. You can chunk up bike design into fairly separate parts - geo/wheel path, kinematics, stiffness.. to a point anyway, they're still very interconnected obviously. But you can nail one and not the other. Ski design is holistic voodoo, everything is connected to everything else.
The funny thing is the same applies to bikes.. Over the past decade or so, pretty much every individual dimension has been argued about, but at some point everything needs to be looked at as a whole unit.
That was my comment in that thread
That was always my dream set up, S4 triangle with S5 seatstays.
Those bikes also work well with the mullet link but run it as a 29er. Steepens everything up and gets that BB off the ground, pedals much better.
Reading this discussion makes you wonder what the perfect geo really is. For enduro racing, for example, a shorter bike is almost always faster (Rude, Moir, Melamed..) because it just fits better on those tight turns and makes swinging around them easier. Shorter chainstays on larger bikes also make the bike turn better on tight stuff because the rear follows better around a turn, and the turning radius is smaller due to shorter WB. However, for high-speed applications such as DH (and also modern enduro racing to an extent), a longer rear end offers more stability and better handling characteristics. Managing tight and janky turns isn´t a problem in DH since those just don't occur anymore that often with the development of the sport. Also, for less-experienced riders, longer rear ends make a lot of sense, as they can considerably calm down the handling.
Not only in terms of sizing, but also in the general type of bike. Take Trek’s lineup with the Slash and the Fuel LX, for example. If there were still teams riding Trek, I’d bet quite a few riders would switch to the Fuel LX for exactly that reason: still very capable and forgiving, but quicker and lighter through turns.
Riders at this level can definitely hold onto the bars when things get a bit rougher.
@scrubaddict
Longer rear end gives more stability and confidence which means you can be more playful on trails or speeds that are on the edge of your comfort zone.
Longer rear end climb better. I love them for tech climbs as there is way more traction and you don't have to put energy into resisting the bike looping out. Sure trials hops are probably harder but who does that?
Why is faster the only metric?
I took a Pivot ebike up a real steep slope. The only tiring part was resisting the bike looping out. Seemed like a huge design flaw.
I'd be curious is racers would prefer a shorter balanced bike, or just short chainstays.
There's not really a perfect geometry based on the fact the personal preferences will come into play..
I have a proposal for the future, can we define flickability for bikes as having a relatively low moment of inertia for the rear end? Ie, less resistance to changing direction.
Most people that use that term are referring to the general inherent instability of a given geometry/design.
I feel like we described the same thing in different ways, instability means less resistant to changing direction, or easier to rotate. When we talk about flickability, that usually refers to how easy it is to pick up and move the rear end of the bike, flicking it out so to speak.
Specialized Enduro team has also chosen the Stumpy over Enduro for years now. And at least some of the athletes in the Forbidden team raced on the Druid vs the Dreadnought. Modern "trail" bikes seem to be all the rage in enduro nowadays!
I am curious if anyone here has experimented with different widths of stem, like the part that clamps onto the handlebar. Do stems with a wider clamp end up making the bar stiffer? Logically that would make sense but im not sure if its enough of a difference to notice.
The Oneup DH direct mount stem has front clamps that can be run either wide or narrow to get more stiffness or flex. I've got one on my V10 but haven't played around with it. Probably pretty hard to tease out any really difference but then again I'm not a pro doing hundreds of offseason laps to test and bracket.
Of course a wider stem will make the system stiffer, but not measurably. You're clamping down on the, by far, thickest part of the bar which is subsequently also the stiffest. And you're loading it 300+ mm from the clamping point. Adding a few mm on the clamping width will change the loading distance in the range of a few percent Given what the movements of the average handlebar are, you won't notice a few percent. Getting tired through the run, different grips, moving your hands inwards or outwards will produce a bigger effect.
Or, a really compliant bar, even clamped very widely, will still be much softer than a stiff bar clamped narrowly.
6'5" here. Trail bikes in XL/XXL with F:R ratios less than 1.9 are hard to come by. I had a XXL Hightower V3 for a bit which had a 1.96 ratio. When the F:R ratio gets that extreme it feels anything but playful. I mean the front is easy to lift but having to put so much weight on your hands in corners and worrying about front wheel traction all the time doesn't give an over all playful experience. The bike actually felt cumbersome in low speed corners and sketchy at higher cornering speeds. Not super fun when you feel like you're having to walk on eggshells with the front tire grip.
If I want a playful bike I'm looking for a few things: steeper head angle, shorter reach and the stays to be just long enough to feel balanced. I found the size smaller XL HTV3 to feel way more playful which proportionally longer stays (1.9 F:R). Buying a bike with a long front center then wanting short stays to make it playful makes no sense to me.
If you scale down your XXL hightower chainstays relative to our difference in heights, it's like me riding a bike with 408mm chainstays (i'm 5'11"). You've been riding bikes with chainstay lengths on the wrong side of playful for your entire mtb life, so it makes sense that longer chainstays feel more playful. I love short stays but I would hate 408mm with a passion. it would be so restrictive.
If I choose a chainstay length that I don't think is playful, such as 450mm, scaled up for you is damn near 490. You might find that bikes with 490 chainstays lose a little bit of playfulness. You've still got the advantage of being higher above the axles though - scaling up the wheel size from me riding a 29", it's almost like you riding a 32". Have a ride of a 32" bike with 490 chainstays and see what you think - you'll be experiencing roughly what a mid height person considers "planted" haha.
That sort of chat really does illustrate why proportional FC:RC is important though.
„You might find that bikes with 490 chainstays lose a little bit of playfulness.“
[citation needed]
Keyword being "might".
Average sized riders have the advantage of choice.
That's why I typically try to discuss it in terms of F:R ratio rather than millimeters. My complaint is really against the industry being so conservative on chainstay length on the XL/XXL sizes. Trek, Specialized and Santa Cruz all make XXL bikes with huge front centers but then keep the rear way too short. The XXL/S6 Levo has a F:R ratio of 2.0! They keep growing reach (I don't need a 530 mm reach) and the ratios keep getting worse and worse. I just ordered a Mondraker Crafty primarily because it comes with 465 mm chainstays (1.87 F:R).
The real struggle is for them to fit even longer bikes in already crammed bike boxes...
Did you imagine if most of this end up coming down to a matter of logístics?
They can nip 10 mm from the front and put it in the back. The total bike length stays the same, ratio is also improved.
That's exactly what I'd like to see from the three brands I mentioned. I'd have snatched up a Vala with 515 mm reach and 460 mm stays.
How does massively growing rear-center impact suspension design? Longer swingarm => larger leverage ratio, no? Compensating for larger-than-small R-C changes between sizes must be a fairly expensive R&D exercise?
Must bikes/brands with size specific chain stays/rear centers just move the pivots further back on bigger sizes. So all parts/ links/ratios etc are the same.
A lot of brands achieve a longer rear center by just moving the pivots further back on the front triangle. There's some obvious constraints with how far you can go with that.
Technically the kinematics across frame sizes would have to be different anyway. Antisquat is dependant on the height of the CoG which is different depending in the rider height (and position).
But yeah, that would make bikes even more expensive.
What happens quite often is that the actual chainstay length doesn’t change. Instead, the position of the bottom bracket relative to the rear axle changes. That way you alter rear center / front center while keeping the leverage ratio (and rear end) the same.
More rarely, the main pivot location itself is changed to accommodate different chainstay lengths. But when you do that, you also change the leverage ratio, as mentioned.
Since each size already requires a different mold for the main frame anyway, it’s often easier to keep the stays the same and simply adjust the main frame.
Example Trek: even tough they have different chainstay lengths, the actual chainstays are the same.
Post a reply to: Modern Geo Talk: Chainstays, Stack, Reach, and Bitching About It