Normal Amount of Crank Spin? New BB & Crankset

Triathlon Forum
1

I recently installed a 30mm spindle Rotor Powermeter crankset with a Rotor BSA30 bottom bracket and it doesn’t spin as freely as my old GXP wave washer BB/crankset. I made sure not to overload the pre-load adjustment collar, but even if I back it off allowing some lateral spindle play, the crankset spin is unaffected. I’ve heard that spin tests are not really valid because it’s not under load but wanted to get some more eyes and opinions on this.

https://youtube.com/shorts/7Yo0Cb_SHdw?si=6ZRyvbES-kwu2I7d

2

I’ve heard that spin tests are not really valid because it’s not under load

This is correct. Cranks that spin very freely do so (largely) because they have very little seal drag. All we can tell from the video is that there is definitely some degree of drag on the crank. There’s no way to tell if this is just seal drag or something more impactful, because the input wattage to spin is so low.
Turn the cranks by hand. You should feel a very small amount of drag, at a consistent level throughout the full rotation. If it feels grabby or stiff, there may be a problem. But it also might still just be the seals, so if it isn’t really apparent there’s a problem, ride the bike for a bit and then check again.

3

I’ve heard that spin tests are not really valid because it’s not under load

This is correct. Cranks that spin very freely do so (largely) because they have very little seal drag. All we can tell from the video is that there is definitely some degree of drag on the crank. There’s no way to tell if this is just seal drag or something more impactful, because the input wattage to spin is so low.
Turn the cranks by hand. You should feel a very small amount of drag, at a consistent level throughout the full rotation. If it feels grabby or stiff, there may be a problem. But it also might still just be the seals, so if it isn’t really apparent there’s a problem, ride the bike for a bit and then check again.

^^^^This

If you want it to spin longer just go back in and remove the seals and all that pesky grease that’s gumming things up.

Back in the way I used to have a Campy wheel with cup-n-cone bearings. If you left it a little loose and under greased it would spin forever and even a paper clip on one of the spokes was enough to get it to move. It was an impressive demo, but that setup would be much worse than sealed cartridge bearings for on-road use.