Do I need to replace bottom bracket and/or cranks for road-to-fixed conversion?

Question

I have a vintage race frame with a Shimano Dura Ace 7400 series double-ring crankset on a Shimano bottom bracket of some kind.

I intend to use the frame to build a fixed gear bike. As I understand, these road cranks are different from track/singlespeed cranks in terms of alignment, so I would need to replace them. Is that very necessary, or is simply removing one of the chainrings enough?

If the crankset is to be replaced, what about the bottom bracket? Will the existing bottom bracket fit, or are BBs used for single-speeds different in some way? The only difference I can imagine is the width of the part for crank attachment.

Thank you!

Answer 1

It's impossible to say for sure, but it's fairly likely that you'll be able to simply remove a chainring and you'll be fine. You may need to move your remaining chainring to the outside of the spider or vice versa, but that'll usually get you pretty close.

If that doesn't get you close enough, you might be able to replace just the bottom bracket for one with a shorter or longer spindle, but you shouldn't need to replace the entire crankset.

I believe that some people also add some spacers at the rear to get the alignment, but I've never needed to do that personally so I can't speak to it very well.

If you already have the rear wheel, the best thing to do is just put it on and see if the chain lines up. That'll give you some idea of how close it is.

Answer 2

If you haven't yet run into Sheldon Brown's Fixed Gear Conversion page or RJ's videos, it should help

• https://www.sheldonbrown.com/fixed-conversion.html

A couple things, just in case they're helpful:

• road bike cranks have longer crank arms which can lead to pedal strike while taking corners
• road bike cranks typically use a 3/32″ chain where single speed cranks use a 1/8" chain
• the geometry on road bikes are typically different than that of track bikes, which can limit your options

good luck!