Originally Posted by
jcb3
So the SR Super Custom would be a new crank or is it the existing crank and you were able to extract the portion of the spindle that broke?
If you can salvage the crankset, as @
due ruote said, measure the existing spindle - try total length minus the threaded (male) portion of the spindle, if there is one. That will give you a starting point.
If asymmetrical ( drive side different distance from race to end than non-drive side - which is likely on these Treks), see this
https://www.sheldonbrown.com/bbsize.html
Scroll down to where the diagram of the spindle is, with the table below. That should bring you home.
Not much downside being wrong here, ultimately you will probably use the other one some day. I usually start out wider (127) and see how the bike shifts. Too close in and either the smallest front chainring rubs on the frame or you will get chainrub on the middle front chainring when on the smallest front chainring and are in the middle rear cogs.
You could also try to figure out chainline, but I'm an engineer and can't figure it out reliably - I just do trial and error (hence a drawer full of different spindles)
This is why I just focus on the drive side end of the spindle. You do have to make sure you buy the correct B.B. shell width, but otherwise it’s the driveside spindle end that matters most for chainline, and the NDS matters comparatively little. If your OEM spindle was Xmm and you buy an Xmm cartridge unit, you may not get the correct driveside spindle extension. At least that’s been my experience. Also remember that if you goof slightly and get one that’s 1-2mm too short, you can add a shim to bring it out a bit.
if you want to use your original cups and just replace the spindle, posting the dimensions of your old one may shake a replacement out if the bushes.