SO I have a motobecane fantom cross pro with hollowtech II BB and cranks, and to make a long story short I got it used and cheap but all together have put in an additional $250 (which includes the brand new 165mm tiagra cranks i bought) to get it running right, (a much discounted price due to my bike shop being a notforprofit, and I have good rapport with the mechanic that runs the shop). Anywho, among the other issues he had to correct the bike came with an FSA BB, and Tiagra cranks. He said there was some play b/c the parts don't quite match up and I should replace the BB at some point before failure occurs. My question is, is it possible to use a higher quality shimano bb with the tiagra cranks? for instance, a 105 or ultrega bb, or is it not even worth the extra coin? My humble internet expert theory is that the quality starts with Tiagra, and the parts are only lighter as you go up in the price range. thoughts?

quick search says up/down compatibility is fine.

I like the Ultegra level, with 105 on my workhorses bikes. slight finish and weight improvements.

Yep, as long as it's hollowtech II and the right width you're golden.

THanks for the help. My next question, would this be italian threaded? anyone maybe know what to look for in a bb replacement? I don't know what width to get either. The BB cups? say mega exo BB 8000/6000 and BC 1.37" x 24T.

by https://www.bikesdirect.com/products/..._pro_ti_xi.htm , you need 68mm width, 1.37" x 24tpi (English threads).

MegaExo is the FSA brand outboard BB.


99% it's English threading. if you're uncomfortable email bikesdirect.com for any specs not on the website.

just pick the level of Hollowtech II that you want and do a Google or Ebay search for the best price, along with the proper tool if you don't have it already.

i like:



the nice thing about cartridge/external BB's vs. loose ball is that (for many riders) it's an install-abuse-replace item as they are (relatively, $28 for an Ultegra) inexpensive and take about 5min to swap out.

thanks guys. may this conclude my noobly pursuit.