Bicycle Mechanics - BB sizing?

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.



PDA

View Full Version : BB sizing?

idgeek
07-07-04, 07:23 PM
Hi, a newbie here...

I've bought a used GT ZR2.0 frame on ebay to build. I also bought a Shimano Ultegra crankset(6500) for the frame. Now I'm trying to buy a bottom bracket for my project, but I've ran into a problem.

I notice that Uletgra bottom bracket(BB6500) comes in several sizes. So I measured my frame with a pair of calipers. And this is what I found:

the cylinder where the BB would screw in to(I don't even know what it's called) is measured diameter 33.7mm and the length of the tube is 67.9mm.

But the BB comes in 70x118.5, 68x118.5, 70x109.5, 68x109.5.

Which one should I get?

Trek Rider
07-07-04, 10:09 PM
Italian threaded bikes use 70 mm while English use 68.
Doubles use 109.5mm while triples use 118.5.

I would guess that your frame takes the 68 x (whatever crank you have).
madpogue
07-07-04, 10:18 PM
Oh, and that part of the frame is called (big surprise!) the bottom bracket shell.

gruppo
07-07-04, 10:19 PM
You should take the frame & crankset to your favorite lbs and have them install the correct bottom bracket. It will be money well spent.
idgeek
07-08-04, 06:02 AM
Oh, and that part of the frame is called (big surprise!) the bottom bracket shell.

Ha, ha! I'd should've known... :p

Thanks all of ya!
Retro Grouch
07-08-04, 06:42 AM
Double or triple crankset?

If it's a double, you need a 68 x 109.5mm bottom bracket.
If it's a triple, you need a 68 x 118mm bottom bracket.