WTD 165x38 rear air shock
I had a brief browse at rear shocks recently, as I was toying with trying an FS ride to see what all the hype is about...
Is it not the case that size is only one part of it and that you also need to consider the design of the bike suspension the shock is to be fitted to. IE. Linkage ratio and whether it is rising or falling rate.
As I understood it both compression and rebound tune, along with air can sizing all play a part. If these are way off then the suspension will not be able to be set up properly or perform particularly well.