Originally Posted by motorizedmatt
Honestly, the rear sprocket is offcenter ever so slightly, maybe 1-2mm. It doesnt make the chain go tight loose, tight loose though. It's really only noticeable if your going above 10mph and look down at and you can see it moving very little. And there are no bent teeth and the chain fits well on it.
The amount of eccentricity that causes tight and loose spots on a fixed gear or single speed bike is usually not even visible. You'd express it in tenths of a millimeter at most. But if the tight spots are too tight, they can cause noticeable resistance in the pedals, break axles, wreck freewheel bearings, etc.
If you must have runout in your drive sprocket, bias the chain tension towards looseness, so that it does not tighten excessively at any point in the wheel's rotation.