Bottom bracket sizing question

Richard.S

Hi,
I am buying a new frame which has a BSA 73 BB shell.

I have looked around and many bottom brackets advertised state they are BSA 68-73
What do these figures refer to: the diameter of the hole, or the width of the shell from the drive side to the right side?

Thank you all in advance.

larkim

I may be wrong, but I think 68/73 are sold as universal road (68mm) or mtb (73mm) with the difference being the spacers used when fitting. That could be rubbish though...

wilberforce

The 68mm and 73mm dimension measure the width of the bottom bracket on the frame of the bike with no BB installed, simply the width of the shell. Most road bikes that use a threaded bottom bracket measure 68mm wide and most cross country/trail mountain bikes measure 73mm

.... all info supplied courtesy of Google

Richard.S

Thank you for the explanations.
I try not to search for answers outside of forums, as one never knows the validity of website information.

I trust the answers from forum members

Thanks.

Alejandrosdog

Richard.S wrote:

Thank you for the explanations.
I try not to search for answers outside of forums, as one never knows the validity of website information.

I trust the answers from forum members

Thanks.

LOL i wouldnt trust half the answers in this place. (unless the answer is from me of course )

swod1

if your new frame is 73mm then you wont need as many spacers on the bb when you fit it.

it used to be 2 on the drive side and 1 on the none drive side but newer frames you sometimes only need 1 on the drive side or none just depends on the chain line etc.