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What's a BB?

480 Views 5 Replies 5 Participants Last post by chas_martel, Jun 16, 2009

Robby22

Discussion Starter · Jun 14, 2009

sorry lame question here, but I keep reading about bottom brackets and I'm not quite sure what one is. I've looked at pictures of them and my best guess is a thing inside the frame that the pedals and crankset connect to... and please also tell me why these seem so important and are a big topic of discussion.

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f3rg

· #2 · Jun 14, 2009

A bottom bracket is a bearing and spindle device that goes through the frame. The crank arms are bolted to the spindle, and the spindle spins on the bearings.

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kapusta

· #3 · Jun 14, 2009

Robby22 said:
sorry lame question here, but I keep reading about bottom brackets and I'm not quite sure what one is. I've looked at pictures of them and my best guess is a thing inside the frame that the pedals and crankset connect to... and please also tell me why these seem so important and are a big topic of discussion.

The bb is the spindle (axle) that the cranks attack to, along with the bearing that it spins on. It is not really part of the frame, it is a part that treads into the frame.

One reason they are a big topic of discussion because there are many different kinds of bb's to go with different kinds of cranks.

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Bikinfoolferlife

· #4 · Jun 14, 2009

In addition to what the others said, the bb can be important in terms of chainline adjustment or it can be a source of creaks (or sometimes just appear to be the source of creaks). If you want to read up a bit, this is a good start www.sheldonbrown.com/bbsize.html