This is an old post, but a lot of hog wash here....I've been riding touring bikes (HD) for almost 15 years and ride them like I stole them. Single side rotors (13"+) with 6-pison calipers or dual calipers stop the bike just fine. I've never had a problem running 13" w/6-piston caliper or 18" w/ dual 3 piston calipers.