I figured it would be good to start a new forum topic dedicated to arguing about chainstay lengths instead of derailing the tech rumors thread even more. Sorry about that btw. 😅
I guess I'll throw my hat in the ring first. First off, I don't think proportional chainstays are a marketing gimmick. For instance, imagine yourself riding your current bike, but with a 10mm chainstay, and then with a 1000mm chainstay. Both would probably feel weird and compromised, right? Personal preference and terrain undeniably affect how long each person likes their CS, but there is definitely a sweet spot for CS length, and I believe this sweet spot generally scales by how large your frame is. The way I see it, you weigh the bike with your feet, so your foot position relative to the BB is key to how the bike handles.
I still don't know why a physically longer CS length (i.e. a chainstay arm that is literally longer, like the one found on the Specialized Enduro) paired with a short rear center would ride like a bike with a longer rear center. I looked at two bikes w/ physically longer CS lengths that were brought up in the tech rumors thread as benchmarks: the Specialized Enduro and Merida OneSixty. Their axle paths were both quite forward, and the bikes had very different anti-rise, anti-squat, and leverage ratio values. There's nothing about the bikes kinematics-wise that leads me to believe there's something the physically longer CS is doing to make the rear center feel longer; the bikes' kinematics don't have much in common either. Maybe there's something flex-wise? Or maybe OP just really gets along with the bikes' geo, which is totally cool too. Either way, hopefully someone can chime in on that.
Thanks for the discussions as always. 🙂
Perhaps it's my history as a trials rider, but I'm short stays for life. Though it's kind of a moot point as i can no longer ride due to MS. Even at 6'7" 2m, my homemade DH bike has 16 3/8" 416mm chain stays for it's 9 1/2" 240mm of travel.
regarding the "marketing gimmick" comment the guy made in the other thread, I think his point was that the majority of companies claiming "proportional" rear centers only have a difference of 5-15mm max between smallest and largest sizes, which isn't enough to truly be proportional (depending on how much reach increases). the idea is to scale front and rear centers linearly for F/R weight distribution to be constant across sizes, so any company that doesn't do that (forbidden is the only one that does afaik) is using the term for marketing purposes rather than to describe a proportionally consistent bike design.
Thanks for clarifying! I just replied to him in the other thread that he made. I think his thread is more useful since it covers more aspects of geo than just CS length, so I'll probably be moving over there.
I think also that mtb riders as a whole are a somewhat conservative bunch. When I think of "proportional" rear center lengths being smaller movements than ideal I just see brands dipping their toes in and getting riders used to the idea of something.
You could go MORE proportional and have the range be closer to 40mm difference in RC length between small and XL (10mm steps between sizes) but then that might cut off more riders than it gains.
Think of how long it took riders to get comfortable with the current geometry style. Mondraker introduced their "forward geometry" putting emphasis on longer/lower/slacker in 2013. Some brands are still just getting around to it and some riders are still unconvinced.
How many folks riding their 2019 full suspension bikes with 435mm chainstays who have a hard time manualing and are now starting to look at a new bike are going to feel more comfortable with a 475mm chainstay? How many of them are going to be compelled to buy a brand's bike with one of their selling points being "we're making something you can't do but would like to be able to do even harder."
Most riders are not seeing the benefit of a long bike as they rip down black trails. They're enjoying blue trails, fighting the length of a bike as they're trying to bunnyhop a small branch in the trail, and being sort of scared of that one switchback coming up. Considering the cost of many bikes these days vs wages, I think the new-bike purchasing group maybe skews a little older than it did previously. Does ol' Soreback McWilliams want a bike that's going to be easier or harder to manual?
I don't disagree with longer RCs being beneficial for many riders. I don't think that most "proportional" RCs are as proportional as they should be. But I do UNDERSTAND why brands are hesitant to make that leap all in one go. I suspect we'll see greater "proportionality" of RCs offered from the majority of brands in the '27/'28 crop of bikes. We might just be half a bike generation early yet...especially when you consider that a lot of these bikes released today were designed in 2023 or earlier.
I think the proportional movement leads to comically long RCs on larger sizes but I am glad there is a variety of choices across the industry.
is this about rear centres or chainstay lengths?
BB to axle
or
pivot to axle?
some bikes have a 460-480 chainstay but a 440 rear centre...
Some bikes, like the slash have a short physical stay and short rear centre but it gets considerably longer through the travel.
The argument of 'rear centres' is about weight balance but So much effects it, like fork setup, stem length and who's riding it etc.
This thread is about rear centers. Thanks for catching that, I'll distinguish between those terms from now on to avoid confusion.
To your point, I agree that rear center is just one small part of how a bike handles. Still, I don't see why a physically longer chainstay would affect weight balance, which I'm assuming is a combination between how the tire contact patch is weighed and the rider's CoG. In theory, you could have a chainstay that is so long it protrudes past the chainring, but if the tire's still in the same spot, you haven't changed how the tire contact patch is weighed or where the rider's CoG is relative to the tire contact patch. Making the chainstay that long would probably also adversely affect the bike's kinematics, but you could account for that by messing with the linkage. If anything, making the physical chainstay that long would only cause the axle path to become more forward; the bike would ride like it has a shorter rear center.
Theres static and dynamic rear centre's based on CG/balance That always relates to BB position and where the BB moves to based on travel at the time.
I think your missing the part that a physically longer Chainstay Should move more up and around, vs a short one that will tuck forward thats the whole leverage thing, the pivot moves very little compared to the axle(long lever)
Growing physical stays /growing rear centres, such as many HP bikes make the argeument worse as you can have a short rear centre and physical stay but it grows alot under compression through the kinamatic which can include lower links such as forbidden using a lower rocker (upside down four-bar??) BUT then you run into issues with Chaingrowth etc .
I havnt thought about it much but is there a link between long rear centres and Pedal kick etc?
people forget that changing a bikes rear centre can upset the suspension platform due to leverage. - this was discussed when the 21' Altitude came out, People found it changed the suspension feel quite a bit and opted for the refined shorter setting.
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