For those who have designed a number of full suspension frames or work in the industry, on bikes with size specific cs lengths, is it common to use a unique linkage for each size frame to maintain a similar leverage ratio across the sizes? Or is it more commonly taken care of with a custom shock tune? My thought is that on a smaller bike for example you would have a shorter cs and lower leverage ratio than on the large frame, which is the opposite of what is desired assuming the smaller person weighs less.
Different CS lengths can also be achieved by shifting the pivot locations for/aft slightly with respect to the BB. This changes the anti-squat levels but this can also be made a desirable effent since the CoG height of a shorter rider will also be different than for taller people.
A big benefit is that it enables the manufacturer to use the same part across all frame sizes. The front triangles are different for each size anyway, so different pivot locations don’t really increase complexity.
In general for production bikes the leverage ratios and pivot locations (and chainstay lengths) stay the same.
I do custom everything for every rider, but I’m a weirdo and not representative of anything.
I would approach leverage more from the planned rider weight and ideal shock operating pressure. Use those two parameters to set your sag point (supporting 1g of the rider weight at whatever travel percentage you’d like).
Once your sag is set, ‘pivot’ your leverage curve around that point on the graph to get your desired bottom out and top out characteristics.
CS length/front center length is more about the rider’s weight distribution, which is also another lever to pull for bike handling.
The linkages are usually the same part across all sizes.
Most brands have the same shock tune for all the sizes however some spec a lighter tune for the Small and XS.
Personally, I would want a higher leverage ratio on a small size rather than a lower one.
For very small (children) riders you almost have to go crazy on the leverage just to get the damping circuit (even one with a super light tune) to work right.
I commonly do 4:1 or even higher for kids, and then we just put a bigger bottom out bumper in the shock since they don’t usually need or want 160+mm of travel. Combine that with a light tune and rebound/compression all the way out, and you have a functioning bike.
It’s a little crazy, even a derailleur clutch is a problem for a 40 pound kid when it comes to suspension function!
Thanks for the reply! Hadn’t considered that as an option but that makes a ton of sense
I appreciate all the responses, I realize a lighter rider would definitely need a higher leverage ratio. Not trying to continue to punish small cyclists. My thought was to use a “stock” rear triangle and adjust links or mounting points for each rider’s leverage ratio based on weight and how hard they ride. With sliding dropouts it could leave chainstay length up to the rider and cover a wider audience. Although to @anon91558591 point, there are plenty of cases that fall outside of the bell curve.
I haven’t seen any big brands note different shock curves based on each size so I was curious if there’s more going on behind the scenes