Saddle Position & Crank Length

Sergeant Rock

Recently acquired a fixie which has 167.5mm cranks. My road bike has 172.5mm cranks so I have set up the position on the fixie to match my road bike but have added on 5mm of saddle height to allow for the shorter cranks.

My question is do I need to alter the position of the saddle layback (to compensate for the different length of crank) or maintain the same layback as for my road bike - which I am taking to be my ideal position. I will of course check everything out with plumb line etc. through the pedal axle.

I know these adjustments don't sound much but I've got an iffy right knee and so want to start as close to ideal as possible.

Any advice would be much appreciated.

curium

I'm no expert but I thought you'd want to reduce saddle height to compensate for a shorter crank length?

Sergeant Rock

Me neither but if you fit shorter cranks you reduce the distance that the leg has to extend through when at the bottom of the pedal stroke - therefore to get the same leg extension at the bottom of the stoke I have raised the saddle. What I am unsure of is how much this affects the angle of the leg / knee during the pedal stroke and whether there is a 'rule of thumb' on altering the layback of the saddle to compensate.

amaferanga

I wouldn't worry about the setback. By all means put your saddle up a bit, but I doubt very much that you have your setback adjusted optimally to the nearest mm on your road bike (who has?). If you were to adjust it you'd probably be looking at a sub-mm adjustment.

cougie

I really wouldnt sweat it.

Its 5mm we are talking about here. Do you sit bang right in the centre of your saddle every time, or maybe 2mm forwards or backwards, or possibly tilt your ankle a bit ?

5mm is a tiny distance compared to how long your leg and foot is.

Try your position and see how you get on.