HELP! BB4000 and BB30 crank

pocketrockettb

Hi,

I hope you can help/offer some advice with the following:-

I’m a beginner to cycling and have recently purchased a Cannondale Synapse Alloy Tiagra 2011, size 54cm, with a 172.5mm FSA Omega MegaExo Compact 50/34 crank that sits in a FSA BB 4000 bottom bracket. The 172.5mm crank arm length is causing me some knee problems as I’m short legged, so I want to try a 165mm crank arm length instead.

I can’t find a 165mm FSA Omega MegaExo Compact so I’m looking to buy the Shimano Tiagra compact 50/34 165mm crank set due to the bikes group set being Tiagra.

Firstly, is this possible to fit the Tiagra crank? I assume I would need to also replace the FSA BB 4000 to accommodate the Shimano Tiagra crank but with what I do not know.

Also, I’m sure the Cannondale frames bottom bracket is a BB30, but does this matter as the current crank ‘FSA Omega MegaExo Compact’ doesn’t seem to be BB30!

Some help/explanation with the above would be fantastic.

Many Thanks

Monty Dog

The Tiagra requires a BB for a 24mm spindle whereas the Omega is a 19mm spindle so not interchangeable. I'm presuming that there is a threaded BB30 adaptor fitted to the frame, so it should just be a case of removing the FSA one and fitting a Hollowtech II one.

pocketrockettb

Hi,

The crank fits into the BB4000 so are you saying that the hollowtech II will fit into the Cannondale's BB30 bottom bracket frame and directly replace the BB4000? i.e. the outside diameter of the BB4000 and Hollowtech II are the same so they will fit into the frames bottom bracket?

Monty Dog

Yes - simply unscrew the FSA BB and fit the Shimano one. If you say your frame is BB30, this it probably has a press-in threaded insert fitted to allow the current bottom bracket to be fitted.