depends

Is the spindle length on a bike determined by the frame or is it solely dictacted by the cranks or is it a combination of both? I am buying a used bike frame and need to know how to get the right size of bottom bracket.

the shell width is determined by frame although many of the aftermarket bottom brackets can accomodate either width.

spindle width (or length depending on your perspective) has to be wide enough so the cranks clear the frame but after that, it's kind of personal preference. some people like a wider spindle to get their feet further away from the frame. the caveat to this is that if you go too wide then shifting can become problematic on certain frames.

YR

 

How does 'chainline' fit into the equation?

Thanks, but how does 'chainline' fit into the equation...is that influenced by the frame or is it determined by the cranks. I note that at Sheldon Brown's website he seems to have cranks tied to spindle length, which would suggest that the frame is irrelevant....which has me confused!

the shell width is determined by frame although many of the aftermarket bottom brackets can accomodate either width.

spindle width (or length depending on your perspective) has to be wide enough so the cranks clear the frame but after that, it's kind of personal preference. some people like a wider spindle to get their feet further away from the frame. the caveat to this is that if you go too wide then shifting can become problematic on certain frames.

YR

 

it's just an issue

Thanks, but how does 'chainline' fit into the equation...is that influenced by the frame or is it determined by the cranks. I note that at Sheldon Brown's website he seems to have cranks tied to spindle length, which would suggest that the frame is irrelevant....which has me confused!

with front derrailleur shifting sometimes. if the spindle is too long then the front derrailleeur can have issues at either extreme. it may be tuened to hit the small and middle but have problems getting into the big or you may tune it for the big and middle but have issues getting on the small.

it's not a problem universally across every bike and every spindle length. I have teh same BB iand drivetrain on my current bike that gave me fits to set up properly on my old bike, and it was never quite perfrect. Yet, the original BB on the old bike had a shorter spindle and it worked fine. I only replaced it because my feet kept hitting the stays so I wanted to move them out just a bit. unfortunately, moving them out on that particular frame caused me to lose the ability to finely tune the front derrailleur properly since it had to be adjusted out so much more yet was still mounted in the same physical locaion.

YR

 

Take a look at...

Is the spindle length on a bike determined by the frame or is it solely dictacted by the cranks or is it a combination of both? I am buying a used bike frame and need to know how to get the right size of bottom bracket.

...this thread from a couple weeks ago:

http://forums.mtbr.com/showthread.php?t=5157