i don't have much knowledge on this issue but just a wild guess. If one use spacer, shouldn't the wheel be road force balanced WITH the spacer? During the road force balancing, there is a load on the wheel which put force on the mounting surface. When you run a spacer, the effective mounting surface and the load bearing centerline of the wheel would be different than without the spacer, right? Don't shoot me guys, just guessing here. cheers.
