Need Help with my First Fixie
 

I'm in the process of building my first fixie. I took the bike apart, and I realized that I need a new bottom bracket. How do I know which bottom bracket to buy? Are there different sizes? Also do these come with bearings because I need those also? I have never worked with bottom brackets before so any help would be greatly appreciated.

take it to your local bike shop.

this too
http://www.sheldonbrown.com/gloss_bo-z.html#bottom

the bottom bracket you get is determined by the crankset you are going to use and the threading of the frame. Measure the width of your bottom bracket shell. If it is 68mm, it is most likely English threading. If it is 70mm it is Italian.

What cranks are you going to use?

On a fixed gear, the manufacturer of your crank should have a recommendation or a bottom bracket size. (For instance, Pake recommends a 107mm BB for their cranks.)

If you buy a modern sealed bottom bracket, that IS the bottom bracket / bearing assembly, so you shouldn't need to buy anything else (except maybe crank bolts, some cranks don't come with those.

If you decide to DIY at a bike coop, they may have the old school bottom brackets with bearing cups and bearings and the spindle that you can assemble. It's pretty easy to do, but probably not worth it.

If you've got the standard 68mm English threaded bottom bracket, buy the Shimano UN54 Bottom Bracket in the appropriate length for $25 or so, and you should be fine.

God help you if you've got a French bike with a French threaded BB. (Or just take it to a skilled mechanic and have him thread it for an English BB for a few bucks.)

can you re-thread that?!

what kind of frame is it, it all depends on the threading. if you have english or italian threading you can find bottom brackets all over for fairly cheap, no big deal. english bb's are 68mm and italian are 70mm. french are ****ed, the only bb's made to fit french threading are by phil wood i believe and i think they run somewhere around $250. just find out what size threading it is

Yes, you can re-tap English threads over French threads. It's not the most elegant solution, but it can be done. - http://www.cyclingforums.com/archive.../t-358763.html

Other alternatives are to buy the Phil Wood French Threaded BB/rings for $$$, or to "chamfer" the BB and use a threadless BB.

If it's your first fixie though, find a bike with a standard BB, buy the Shimano UN54 sealed BB (in the right length) for $25 or so (get the right installation tool if you need that), and call it a day.

A few years back, I was able to order a Sugino French thread bottom bracket from my lbs for about 25 bucks.