Originally Posted by
Carbonfiberboy
Good points. But why move back with shorter cranks? When my stoker went from 170 to 151mm cranks, I tried doing a KOPS but her power dropped off. I moved her saddle back to where it was and that seems to work better for her.
I'm thinking I need to develop some intelligent way to determine where both pedals and the BB should be w/r to sit bone location and set all our bikes up the same way. We have about the same hip angle on all of them.
So I'm personally in favor of forward fits. Mine is quite forward, but I also am somewhat strong (4W/kg) and race. Some people like rearward fits and have no issue putting down huge power from that position. I think it comes down to preference, cadence, body weight, upper body/core strength, fitness, and what kinds of rides the person is doing (crits vs climbing vs group rides vs touring). Generally, the higher the average pedal force per kilo of body weight, the more optimal a forward fit is. You need to be able to counterweight your pedal force without falling forward too much on your hands.
I honestly don't know if there's a reliable way to nail fore-aft (relative to the pedal at the forward position) given how variable the optimal position is. But I think Steve Hogg has a method to get within a reasonable ballpark for most people. And from there it's just about tweaking. If the rider is consistently sliding forward or bobbing or jumping out of the saddle, they might need a slightly more forward position. Too far forward is more obvious: Quad overengagement and numb hands.
That being said, I think saddle fore-aft is a power/aero optimization problem. If moving the CoG relative to the pedals within a reasonable range causes pain to appear or disappear, that's a red flag.