Shorter BB spindle to fix chainline?
 

I converted a cheap-o department store bike into a beater single speed. The only problem is the chainline really sucks. I'm using a single-speed Shimano cog in the back, and a chainring on the middle-ring location of a triple crankset. The problem is that the chainring is too far from the frame. I'd like to bring it closer and I think a shorter BB spindle is the best idea. Short of taking the cranks off, how can I tell what length I have? If you had to guess, what length BB spindle would you choose to move the chainline ~5mm closer to the frame?

Thanks!

http://img5.imageshack.us/img5/5199/img00098q.jpg

is it possible to use spacers to shift your rear cog out?

I dont think so- it's a single speed freewheel.

I don't get it, can't you just pull off the cranks and measure the BB with some calipers?

Just get a bb with a spindle 10mm shorter than the one you have now :rolleyes:

This is exactly what the OP needs to do.

Assuming it's symmetrical. For example 110 shimano cart to 107 bb results in the exact same chainline.

Gotta guess that's it's not symmetrical too? Not fair...

Do you know what your current chainline is?

The normal chain line is 47-48mm from the center of the ST to the tip of a tooth on the big ring. Measure from the side of the ST and add half the ST diameter.

The short answer is that there's no simple way that I've found to estimate chainline based on BB spindle length. The long answer is that, if you get a shorter BB spindle, you can probably make it work just fine, within a couple mm. Is there any option for respacing and -dishing your rear wheel to fix?