You've really only got 2 choices (not factoring a Dura Ace bb set into the mix which is 109mm). For a 47.5mm chainline, you'll be using the 112.5mm length. For a 50mm chainline, you'll want the 116mm length. Run the shortest you can get away with - especially on a single speed - for the narrowest q-factor.Winky said:I've pulled the trigger and am finally ordering a Karate Monkey. I have an XTR crankset I want to use to run this puppy SS. What spindle lenght do you use? It's a 20" frame and old XTR cranks (952's) thanks for the input, I'll post when I'm done.