I made up spacers to center the rear wheel in the new SRX-6 swingarm. I checked and re-checked my measurements, and it’s still off by perhaps 1–1.5 mm. That’s a functionally insignificant deviation, and even within factory production tolerances, probably (well, almost definitely, for a ’70s Spanish bike with a frame made by Monfort). Frankly, it’s probably within the range of accuracy for my measurement as well.
The big spacer on the brake side is probably chunkier than it needs to be, considering that its diameter is larger than the mating surface on the brake panel. I might do something about it at some point, but then again, I might not.
