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Glad I took a look at this... Informative thread .. As I do more research into this, I'm thinking that a longer CS might be what I'm looking for in a bike. Front end grip has been an issue for me as I tend to ride with a bit of a rearward weight bias..
It's nice to see people looking at frame geometry as a whole. For so long, it would be like people would focus on one number without realizing how other things might need to change with that..
Also, I can't help but wonder if the first decade of getting 29ers to feel like 26in bikes set back the development curve..
But then do n't forget the variable of taller bars vs flatter bars. If you're stacking spacers or stem height, then the bars come back. Then you also have Bar Roll, which for me makes a much bigger difference in how the bike feels. If I my bars rolled back, my elbows flatten and I find myself off the back. Slightly forward (and pared with a resonable up and backsweep), my elbows come up and I can attack the front of the bike.
I mean obvi Jackson saw my set up and it's working well 🙃
I;ve also found that for me personally the new style geo's tend to require an attacking riding style, and holy crap can they make you fast. But they mute everything, dumb stuff down, and require a pace that makes the sudden stops way more brutal.
Posted by noideamtber:
That's nonsense though, and nobody else I've ever talked to considers that word to mean that. There's no way to define that length for a virtual pivot bike in a way that makes sense unless you want to pick and choose your definition of what a chainstay is and what the word means for each suspension layout. And that kinda means the word has no definition at all.
A DW link bike is topologically identical to a horst link bike, so either the chainstay length of the horst bike is only a small handful of centimetres long because it's the distance from the axle to the chainstay pivot, or you include the other frame member too and arbitrarily say that the chainstay length is defined by the pivot connecting the main frame holding the bb to the adjacent lower frame member... but then you're including the short link for the DW link bike too. So Giant's Maestro has longer chainstays than an Ibis with DW because the lower link is mounted in a different location? Where's the logic there? How is that a useful thing to define?
And if you're going to do that, because as you say it affects the AS, AR etc, then maybe we should consider the switch infinity. With switch infinity simulating a lower link of infinite length, then by your definition then the chainstay length of a yeti is infinite. wow, that's pretty long. What about high pivots like Forbiddens? now your definition of chainstay is unfortunately defining the seatstay, because the seatstay is doing the heavy lifting in defining the suspension behavior and wheel path, while the chainstay has no definable length, it's just pulling on a link to actuate the shock. What about I-drive?
Every time you mention this random ass definition of what a chainstay length is, i can't help but think about how it doesn't make any sense and how everyone you talk to is going to misunderstand you anyway. The fun thing about language is that words mean what people understand them to mean, not what you want them to mean.
it's almost as physics dont exsist to you........
Have you ridden a high pivot bike? Moving the damn pivot changes the bike.....
Bikes with Bone links(such as DW/Giant) are less effected depending on link length + upper link as the axle path can be controlled more.
I almost wish I never Worked on Race Car suspension as a job for 15 years + contract Job's in the RC Industry for a couple of brands - It's like explaining the meaning of life to a new born here.
Side Question, Do you notice Offroad cars have long Arms and road cars have short arms?
2nd question, what happens when you have 3 rocker/pivot locations?... Long lever from the seat stay and short lever on Shock side (which means frame pivot is Closer to the shock pivot) Do you know how leverage works?
The picture below doesnt care if its a Shock or a frame pivot, It's all about triangles.
But hey. Your right and physics are wrong.
Cant wait untill we debate Dynamic ride height vs static and how the bike's CG is effected by it + the Puzzle of suspension Tuning that effects it aswell - That'll make your head explode then as theres sooooo much going on.
Oh ok you're one of those. Cool.
Please define what you consider a "chainstay" succinctly in a way that actually covers all suspension layouts.
I understand suspension dynamics and the concept of leverage quite well. The final year of my degree was mostly concerned with mountain bike suspension design and a fair amount of my experience in engineering has involved linkage systems. You're just assuming I'm a moron because i said you had a shit take on something, and I'm a guy on the internet.
Nobody in mountain biking understands that word to mean what you insist it means, and I doubt you can even define it properly.
can we agree that there are two different ways that chainstay length impacts bike handling and performance? it matters how long the chainstay is from axle to bb as the rear center figure. it also matters for suspension behavior how long the axle to pivot point is.
i don't know how much this matters but there does seem to be a distinction that is getting muddied by a singular term to cover both instances...
I thought we were discussing chainstays, not kinematics...
I mean, changing CS length will have an effect on suspension since you are changing leverage ratios. At least that is what I think I have seen people talking about…
Yeah if you have adjustable chainstays then you're basically adjusting the length of the lever that actuates the shock, so lengthening your chainstays will slightly decrease your spring (and damper) rate at the wheel, while correspondingly giving you slightly more travel.
It's pointless to consider the actual length of the lever, because it doesn't physically exist, nor is it possible to calculate the change in leverage without considering the linkage system as a whole. It's totally possible to build a bike where lengthening the chainstay would decrease travel and increase spring rate, but given how constrained the suspension is by the drivetrain, we would never see any weird linkage designs that actually work that way.
Your lost in the sauce bro.
People are trying to discussing geometry, specifically reach stack and FC/RC and your dragging suspension into it.
We know suspension kinematics change when you change any member of the linkage, they are just trying to discuss it in an isolated scenario as its simpler. No need to go swinging your "i worked in suspension for 25 years" dick everywhere.
See, when we talk about chainstays we should be describing the physical object, like the down tube, or seat stay. When talking about Geometry numbers, which are mostly virtual measurements, (think reach, stack, front centre, seat angle etc.) That's when we should be saying rear centre. Long chainstays for me is a misnomer, as the physical object is not always correlated to the axle-bb measurement. I don't get why we can't agree as a community to use these terms, I mean it's not like anyone has ever gotten reach mixed up with the top tube length?
I'm curious why we don't see modern XC bikes with more of a long chainstay/high stack setup. I understand that short chainstay/low stack can keep things whippy and playful, but the cornering stability/climbing grip/more open chest seems like it could be a boon for both actual XC racing and increasing the capability of the bike for recreational riding.
I had two very productive days, getting through a few very long threads I've been leaving behind and this is one of them. So here comes a bunch of rambling.
Proportional chainstays for sure must be a thing. Skis have proportional fronts and backs, it's not like a tall skier will have longer tips and the same tails as a small skier. The question is what is the correct metric. front vs. rear centre I don't think cuts it. Your legs are usually mostly in front of the BB and most of your upper body is as well, so the CoG is in front of the BB (I actually have a calculator that calculates this for a seated rider). Obviously standing up, going down the hill, rotating the bike dynamically (different dynamic sags front and back) will provide a different picture. A picture we can't quite measure. Unless...
What if you wired up a bike with DAQ and found the dynamic sag and maybe, for added measure, the average shaft speed at that dynamic sag. With a dyno you could the extrapolate the force the shock and fork provide to the rider and through that, through the geometry of the bike, you would have contact patch forces. Thus the weight distribution. That way you could compare the weight distribution of a small, a medium and a large rider and see how far out of what they are. Then modify the bikes to balance things out. Heck, even knowing roughly where the CoG is, just trying out what feels better all the way from 400 to 500 mm rear centres across all sizes would have to give an insight, surely different sized riders will pick different chainstays. And the data could also be checked to see the dynamic sag only when leaned over as the fore-aft balance mostly matters there - you want to somewhat equally load the front and rear to have enough grip.
As for low vs. tall front ends. I know of people that handle low front ends and rip, but they DARE to ride that. I don't. I'm very defensive. On my previous bike I even tried clips only to manage one full ride and then scored titanium cheek implants when I crashed. Haven't gone back to clips since (and I raced XC using SPDs for 6 years about 20 years ago). I tried clips because I had a very long bike and tried to get more over the front. What helped later was a much higher rise bar. So much so that with my current bike, I left the steerer uncut and am running 50 mm of spacers with a 35 mm rise bar (I'm thinking about having a 30 mm headset extender made to have decent steerer support). Running higher bars has been a godsend to me.
Think of it this way, it's harder to react from a push-up position (extreme) vs. a crouching, active position. If your front washes, being stood more upright, you'll catch yourself with your foot more easily than if you're hunched over the bars. And running higher bars, bending your arms int he elbows might just bring you lower and load the front more than if the bars are lower (as you want to push yourself away from the bars, to be higher).
I have a friend on a SJ Evo with very good feel about things and I'll try to use him as a test bunny and set his bike up to have the highest and the lowest FC/RC ratio (long rear, steep HA and vice versa) to see if there's a difference in feel. It's not exactly apples to apples as some other geometry values will change, but it's the best we can do on a short notice. It's roguhly a 1,8 vs. 1,9 ratio. Might even throw the 180 mm airshaft in my Zeb too and try it in the short chainstay setting vs. a long one with a 160 mm Zeb, not sure what the ratio change would be on that one though.
I'd agree with you on bar height. I swap between a high stack bike with big risers and an alt-drop-bar hardtail that puts me roughly in a world cup XC slammed flat bar position. And honestly I can get shreddy on either. It really doesn't hold me back. I'd be going the same speed on the same trails if I swapped the risers onto the hardtail.
Lose the front though? On the ground before I know what's happened.
We talked about this in the Tech Rumors thread, but getting more power to the pedals is almost the entire ball game in XC racing, and the main benefit of a lower stack height and more hunched over body position in XC racing is the kinesthetically optimized position for mashing the pedals. Easier to mash the pedals when you’re bunched up in a little ball. Speeds are lower than road racing, so being hunched over for aerodynamics is less important.
"Your legs are usually mostly in front of the BB and most of your upper body is as well, so the CoG is in front of the BB (I actually have a calculator that calculates this for a seated rider)."
I don’t see why this would make the FC/RC ratio need to change as rider height increases, though. In absolute terms, yes — a taller rider will need a longer front center. But unless taller riders are putting proportionally more of their weight on their hands, then we’re still talking about a balance point along the length of the wheelbase.
And I don’t buy that taller riders necessarily put more of their weight on their hands. When I’m riding — either seated or standing — I’m able to do so with an incredibly negligible amount of weight on my hands. Now, if I’m seated and pedaling I’m also counteracting my forward lean with the torque I’m putting on the pedals, but I’m not putting proportionally more torque into the pedals than a shorter rider. (In absolute terms, yes; relative to height, no.) If I’m standing and coasting, though, my weight is on my feet and I”m balancing around the center of the bottom bracket. If my center of gravity was forward of the bottom bracket, I’d tip forward.
You could settle this in an afternoon with two force plates and two riders. Put the force plates under their hands, measure the force their hands exert on the handlebars when standing and coasting. I would bet heavily that both riders put a very similar percentage of their body weight on their hands.
Now, if you put a taller rider on a bike with a proportionally shorter rear center, then they literally have to put more weight on their hands in order to achieve the same balance of weight on the wheels. But in ideal terms, I don’t at all buy that a rider’s CoG moves disproportionately forward as they get higher without seeing some kind of anthropometric divergence.
Some people ride to be fast some people ride to have fun. I don’t think it’s necessarily the case that fast bikes are uncomfortable or that comfortable bikes are slow, but it kind of seems like that’s the general consensus.
XC bikes are not comfortable because they are designed to be fast, but that doesn’t mean that a trail bike can’t be designed to be comfortable and relatively quick. I just think that you won’t be quite as quick on the comfortable bike (on the pedals,) but if you take into consideration how much more fun it is to ride. I feel like the trade-off is more than worth it.
If you had zero weight on your hands, compliant bars wouldn't be such a thing.
Dynamically you push on your hands quite a bit. The nuance of the position on the bike is are you squatting and pushing against a wall or are you doing pushups (fully upright vs. over the bars riding styles, taken to the extreme). The latter loads the front a lot more than the former.
My argument was that FC/RC taken from the BB is not the right point to take the balance from, it's the horizontal COG that's the right one. I'm not saying taller riders don't need longer rear ends, quite the opposite. What I'm trying to say is FC/RC doesn't need to be 1:1 as if it would be, the front would be overweighted as the cog is in front of the BB. Having a 1:1 weight distribution vis a vie the cog should give the most grip. But this is wildly dependant on rider position, so...
After all, in skiing, it's the tips doing the turning and it's loading the tips that acomplishes this.
If I took Suspension design advice from this thread, Id get Fired. There's Far to much to consider When discussing the length of a swing arm.
From leverage and physical length to Pivot placements(and additional links such as Giant/DW or flipped horst) and how they relate to the Bottom bracket AND then you have to take into account Static and dynamic Measurements.(and lets not even get into How chainring size effects Anti squat...)
The one bike That makes an excellent example of Geo is the Gen 6 slash.(when talking rear ends).
The 434(L) static Rear centre looks short but it absolutely does not ride like it at speed and when under dynamic loads/ride height
The harder you ride that bike and the more energy you push through it the better it gets.
I really enjoy reading this stuff and Realising why bike Designers dont listen to Consumers about almost anything.
I wonder what the CS length is at sag? I'm pretty sure with the higher pivot, there is some rearward movement there...
Just did som measurements on my bike for fun (Canyon Strive CFR 2022 M)
The deviation from the manufacturers geo chart and my measuring tape was quite big.
CS lenght, 435mm i geo chart, 442mm measured.
Wheelbase 1262 in geo chart (not specified reach setting), 1271mm measured (short reach setting, so i could add 5 and 10mm to total WB ).
I have never measured my earlier bikes, but what experiences du you guys got regarding this?
But the gen 6 slash definitely pedals steep and tech like a bike with a short rear end. You very much have to weight the front to not loop out.
Glad you brought up climbing in this haha, we really focus so much on descending as a community. Do you run into situations where you are looping out on climbs often? Must be some pretty steep climbs that you are hitting. Personally, I think that the extra maneuverability that a shorter rear end can give works really well for tech climbs, and it helps with bb clearance as well. For climbs that are really steep a longer rear can help for sure.
Climbing more than anything is what kickstarted my interest in bike geometry. My Canfield Lithium descended great on literally anything, but while I loved it climbing ledgy stuff in Arizona, I found it looped out on a lot of steep and extended local climbs here in Alaska. Conversely, I love how my REEB SST climbs here, but last fall in the PNW I noticed how much work it was to keep the front planted on the steep fire roads and whatnot, even though it’s much better than the Lithium in that regard. If I could, I’d actually rather climb on a bike with a longer chainstay and reach, and descend on something shorter.
I would love something that weighs (SP?) right at or just under 30lbs, pedals well, but still has the planted geo of my bigger bike. Obliviously the 36 lb bike is always going to feel more sure footed than a bike under 30 lbs, but I would dig it for my local flat stuff.
Yeah, not to go into it too much but our longest descent trail in town is kind of a joke since it was neutered by input from the on-foot community. It's a great climb up, and it's technically a flow trail on the way down, but you need a bike that pedals great, rolls fast, AND can hold speed through flat corners to make it fun. Maybe an ultralight build on a Transition Smuggler?
There is plenty of choices out there for you all. Its a "trail bike" in the 120-140 range. Lots of options for more pedaling oriented (think Trek Top Fuel) or more fun (Scor 2030) style bikes.
I have a 5010 which sits in your category, in the "fun trail". I'll just say I've been surprised how capable it is downhill coming from bikes in the 150 or so range, but still fun on blues and the "boring trails" because it wants to jump and corner. The geometry these days is so improved. The only time the 5010 gets unsettled is on fast, repeated chunk.
I have a 170 mm bike and honestly on a black trail its a toss up what one to take. Depends how much I want to hang it out as the more suspension has more room for error, but its 5 lbs heavier.
I was strongly considering a Banshee Phantom because I have a Prime and love the overall geo, but those frames are on the heavy side due to the very strong shock cradle design. I wanted a build under 30, which might be possible with the Phantom, but would require a very expensive build. I went with a Chisel FS instead. Its a really sick bike so far, but I do not have the confidence in the front end grip that I would like at this point. Probably just need to ride more.
Biggest thing holding me back from getting an XC bike right now. Had the epic Evo and just couldn’t get on with the handling. Those bikes are designed to where you get the front end grip by running a lot of saddle to bar drop and I just don’t like that feeling.
The chisel/epic vs something like the Phantom or the SST are just completely different classes of bike IMO, regardless of similar travel numbers. I’m sure if I got my SST under 30 lbs, it would be doable on the Phantom as long as you take a step back from the “more is more” approach.
Post a reply to: Modern Geo Talk: Chainstays, Stack, Reach, and Bitching About It