I'm trying to rebuild a bike that I got given free of charge. The bike had no bottom bracket in when it was given to me. How do can I select the optimal spindle width please? I know it's 68mm shell.
Edit: I don't have a local bike shop nearby so I can't take it to one as per suggestions in a previous thread.
Edit: http://www.chainreactioncycles.com/shimano-un55-square-taper-bottom-bracket/rp-prod71369 is the bottom bracket that I need. English thread, 68mm x Y. Unfortunately I'm unsure of what Y should be. By the look of Sheldon Brown I need 47.5mm from the middle chain ring from the centre of the seat post (measuring to that sort of accuracy could be fun). This is where I'm baffled. I could order a sacrificial bottom bracket to measure what size I need by seeing how far out of 47.5mm I am. Is that what I'm going to have to do?
Edit: I do have a crack. It was a spare one I had left over from a few years ago. It's a triple chainset one by SRAM called Truvativ Isoflow.