Originally Posted by
Andrew R Stewart
Unless some one here posts a manufacture's or user's suggestion the way to find out the BB length is by trial and error.
The bike industry isn't a simple plug and play one often
Andy
The real issue is chainline. The biggest factor is the amount of offset in the crank, but other factors, like rear triangle spacing will also have an effect. I think that's why nobody wants to say for sure for every application. Derailleur bikes, fortunately, are a little more forgiving regarding chainline than single speeds.
If I don't know, I'll install the longest spindle bottom bracket I have on hand, install the crankset, and see how it looks. Old bikes tended to have real long BB spindles compared to modern bike standards so, wherever I happen to be working, I can usually find a big old bottom bracket for test fitting. Once I know how much I need to move the crankset in toward the centerline of the bike and I know the spindle length of my test fit BB, determining the best spindle length is easy.