The tire I want doesn't come in the stock 1300 rear size. How far can I deviate from the width and height to maintain at least close to stock. I am getting ready to do a long trip, some interstate, and I don't want to increase my rpm's on the highway too much. I am looking at a 150/80-16, which should lessen the rpm's, but it is narrower than stock. Would this be a problem? What other sizes have you used successfully?