Mountain Bike Reviews Forum banner
1 - 6 of 6 Posts

·
Double XL! Double XL!
Joined
·
124 Posts
Discussion Starter · #1 ·
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.
 

·
pedal pusher
Joined
·
2,712 Posts
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.
 

·
Bicyclochondriac.
Joined
·
14,926 Posts
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.
 

·
Old man on a bike
Joined
·
12,395 Posts
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
 

·
Double XL! Double XL!
Joined
·
124 Posts
Discussion Starter · #5 ·
thank you all
 

·
Registered
Joined
·
3,475 Posts
Robby22 said:
... and please also tell me why these seem so important and are a big topic of discussion.
Think of the forces that are acting on the BB. You are rotating in one plane and bending
in at least two others.
 
1 - 6 of 6 Posts
Top