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My bottom bracket is on its way out.. No longer getting smooth rotation even without chain attached. I was wondering if anyone knew what sort of bottom bracket the frame supports? I've googled but the results are fairly mixed.

Also I assume I just need a special bottom bracket wrench to replace it, is that correct?

Cheers, John

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More importantly, what is the make and model of your crankset? That will determine both spindle type and length. Most bikes accept bottom brackets with a 68 mm shell and 1.37" x 24 tpi threading (with left-hand threads on the drive side.) –  WTHarper Dec 30 '12 at 20:21
    
It's a FSA Vero, 50/34 (compact) apparently! Ideas? :) –  John Hunt Dec 30 '12 at 20:42
    
I'm not a cycling expert.. I'm guessing the only real way to be sure of what I need is to literally remove the bottom bracket and see what size it is? I would have thought there'd be an easier way but Trek seem to not want to publicise what components are in my bike... does anyone have any solid evidence of what's in there? I've read a few conflicting things on the internet.. not sure really. –  John Hunt Feb 12 '13 at 22:35
    
Poosible duplicate of bicycles.stackexchange.com/questions/14450/… –  Benzo Feb 13 '13 at 21:16
    
Before replacing it, try taking it apart, cleaning it thoroughly, greasing it back up and see if it works. Faster, cheaper and leaves you with that warm buzzy feeling of saving money. –  jurgemaister Feb 14 '13 at 14:39

2 Answers 2

up vote 1 down vote accepted

I contacted Trek directly. They informed me it's:

68x110mm square taper bottom bracket.

So there you have it! Hopefully this will help others googling such questions :)

Am I right in assuming this is the same as a JIS square taper?

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9 times out of 10, modern square tapers are JIS and not ISO. –  WTHarper Feb 13 '13 at 19:15
    
I bought this: Shimano BB-UN55 Bottom Bracket British Thread 68-110mm and it worked a treat :) –  John Hunt Apr 12 '13 at 9:09
    
In any case, if you switch a JIS and ISO with a modern cartridge BB, its not really a problem - a JIS crank on an ISO bb sits about a half centimeter further out than it would on an ISO bb, which isn't too much to totally mess up your chainline (of course, the right bb is preferable). –  Batman Oct 12 at 2:39

From Trek's archives and Bikepedia, it looks like that bike has an FSA Vero compact crankset (no mention of the bottom bracket (BB)).

From the Amazon page for the FSA Vero Compact it appears the crank is compatible with a JIS square taper bottom bracket.

JIS square taper bottom bracket is a common type of cotterless bottom bracket, available from many manufacturers.

You'll need to check that the bottom bracket shell sizing and threading matches the BB, too.

You will need a special tool to get the crank off and another for the BB.

See also:

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Also, it will need to be a 110 mm long spindle. –  WTHarper Dec 30 '12 at 21:25

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