I'm sure this has been covered before, but I need help.

How do you determine what size cranks to run? I'm currently riding 2 sizes.

3 bikes: Road bike, Cervelo tri bike and a cyclo-cross/utility trainer bike. I ride the cyclocross on my CT and spinning sessions on Kreitlers for the winter. It has 172.5's The road bike has 175's, I ride it in group rides and most of the time during the summer.

All this time I thought the Cervelo was 175 until I checked. It's also 172.5 I race and train on it during the season. To be honest, I can't tell the difference between the diff. size cranks.

I ride about 5-6000 miles a year, evenly split between the bikes.

I'm 5'9". I know 175's sound long for my height, but I have a 33" inseam and longish femurs. My buddy is 6-2" with the same leg length.

Am I hurting my performance by training on 2 different sizes? I'm guessing it would help if all were the same size. I'm ready to switch 1 or 2 bikes over. Problem is I don't know which to switch. Any ideas or suggestions on how to determine? If I go by feel, they both work.

Thanks