Originally Posted by
hueyhoolihan
spacers can be judged to be appropriate with NO tire, rim or spokes on the hub.
spacers serve to position the hub between the dropouts such that when the cassette is mounted there is sufficient chain clearance between the small cog and the dropout and a match to the rear spacing.
+1
The hub can be correctly spaced out even if it is not laced up to a rim. This is generally correct from the factory, but if starting from scratch there are two simple rules: 1) the cassette/freewheel should be as close to the right dropout as possible without anything interfering. 2) the left side is then spaced out to match the frame's spacing.
Messing with the spacing to fix an off-center is only creating a new problem rather than fixing the real cause of the existing one.