How much resistance should a bottom bracket have to turning?

unixnerd

I took the Truvativ Isis drive crankset off my road bike today, it's going to go onto my tourer which badly needs a new one. Put a DuraAce 7800 triple on the road bike, barely used for 100 quid on ebay :-)

Anyway, I was a little surprised about how much force it took to turn the Isis spindle by hand. It felt like turning something through thick oil. It was very smooth (no grit) and oil was stone cold which wouldn't help it's viscosity. It's not done very many miles either.

Would anybody who's seen a brand new one care to comment? I know it has sealed bearings so only option would be a new one.

jomoj

Hi - that sounds right for a sealed unit, if it was gritty or felt 'notchy' as you turned it then I'd worry. If you add the leverage of the cranks and the fact you turn it at a relatively slow rate then the resistance you feel when turning the spindle with your fingers is neglible.

pete.whelan

That would be the viscosity of the grease and the rubber seals.

You should find it turns a little easier in warmer weather.

After a few miles you won't notice it, as it will have got the grease warmer and so less viscous

unixnerd

Thanks for the advice, I'm hoping it'll be OK when the grease warms up. Just fitted it anyway. The very old square taper bracket that came out had less resistance but was beginning to have a little play too. Must have done about 7k miles though, not bad going.

desweller

It has more to do with the seals on the bearing. They will wear away a bit in the initial stages of use, and friction will drop as a result. The amount of resistance involved is very tiny and does not increase with load anyway.