Originally Posted by
rustystrings61
I have run 17T/19T or 16T/18T combinations on flip-flop hubs for many years with no problems, including the brake pads still lining up and being functional - and that's with the stylish but stupid-for-the-road rear-opening track ends. If I had been wiser and had spec'ed standard forward-facing, slightly-slanted "horizontal" dropouts instead, I'd probably be able to go more than just two or three teeth difference, but hindsight, you know?
OTOH, you might have found that slanted, front-facing dropouts create more problems for brake pad alignment, since the axle (and rim height) rises or falls in correspondence with the slant, in addition to shifting fore or aft.