Chainline: Freewheel vs. cog?
 

On a regular freewheel hub, is there any difference in the chainline between a bmx type freewheel and a track cog? I'm thinking about switching from a freewheel to a bumbike setup while I save for a proper track hub, but I'm wondering if it will affect my chainline which is perfect as it is.

It will have a little difference, but no more than 2-3mm.

there will probably be a little bit of chainline difference unless you spend some time doing the math and getting it perfect. If that's the case, go for straight chainline with the fixed side and let the freewheel be a little bit off.

The 2-3mm that jacobs said ISN'T going to make a difference.

I concur. Depending on the type of chain you have (geared vs. BMX style) there is actually a good amount of play that will allow for the difference in positioning.

cool, sounds like it should work fine since I'm using a bmx type chain and the chainline is about perfect as it is.