Originally Posted by
carleton
Only a 5mm difference?
Again:
The common Track and Road crank lengths are:
165.0mm
167.5mm
170.0mm
172.5mm
175.0mm
165mm and 170mm are 2 sizes apart. This is not insignificant. The footspeed (going in a circle) required to maintain the same cadence between the two is different.
I'm not going to offer advice on what you should do. I just want you to know that your crank lengths are very different. Like the difference between a small and medium sized shirt.
At 100 RPM footspeed =
165mm cranks = 1.727876 m/s
170mm cranks = 1.780236 m/s
175mm cranks = 1.832596 m/s
It's a 3% difference between the first two, and a 2.9% difference between the second two. Seems small, but if you thought about it in terms of gearing (to slow your foot back down), that's roughly a 2 tooth increase on the chainring if you're using 48-51 tooth rings.