175mm or 170mm crank length

[hamster]

I'm 5'7" and run 175 offroad, 170's on road.

I had horrible knee pain touring with 175's. I think this was grinding gears with a heavy load and over-extending the knee.

 

[cannondale king]

i got 170mm's on the jump and 175mm's on the trail bike i can safly say i cant tell the diffrence at all