I am in the process of replacing the cranks, chainrings, and BB for my 2005 Trek 3900. I have heard of 68mm and 73mm cages, and I am confused if either the BB's are bike-specific or not. What I want to know is: are all BB's compatible with all bikes? Are the cage sizes important for cranks to fit or to fit the bike? Anything known about BB's, cranks, and how they all work together would be appreciated. Thanks.
Mtbr's 2016 Winter Biking GearReviews and Roundups
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Thread: Which BB for my Trek 3900?