Gear Combo Guru
Join Date: May 2007
Bikes: road, commuter/tourer, hardtail MTB, touring tandem, cargo, folder
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The poor man's method of measuring derailluer hanger alignment is to find a wheel whose axle has the right size thread and mount that to the derailleur, then do some measurements (the first wheel I tried worked).
With the bike's own rear wheel in place, remove the rear derailleur. Thread the other wheel onto the derailleur hanger where the derailleur would normally mount. You can then measure the lateral distance between the two rims at various points (not the easiest thing to do, but try as best as you can) and if these measurements are all equal then the hanger is correctly aligned. Obviously, both rims need to be laterally true for this to work.
Unfortunately, it's not a very accurate method, but I believe it is the most accurate method you can do at home without a fancy tool.
Last edited by Chris_W; 01-30-09 at 06:48 AM.