Originally Posted by
Bob Dopolina
What is your inseam? Crank length is usually related to that. If you are having knee pain it could be related more to positioning. Have you looked at that? Do you have another bike where you don't experience pain? If so have you compared your position on the two? Are you cleats worn? Do you have a slightly bent pedal spindle or crank arm?
My inseam is 33" and the crank length that works for me is 172.5 mm. The bike I bought had 175 mm cranks but was otherwise set up the same as the bike I had been riding including saddle height and position. Since installing a new crank with 172.5 mm arms, I've had no knee pain on the new bike over about 700 miles. I realize this a N = 1 and the p value is worthless but for me it's significant. The crank I installed, by the way, was a Shimano R700, replacing an FSA compact carbon crank. I was constantly having to adjust derailleur position and tension to try to prevent the chain from being dropped with the FSA. With the Shimano, it has been "set it and forget it," with very smooth shifting and no drops. I wouldn't have thought there could be a difference in two cranks with the same size rings but there is.