So what do you think will provide the least rolling resistance and/or most range: 18" Aero wheels with no covers and Michelin MXM4 tires vs. 19" Sport wheels with ContiProContact tires. They look to be the same width, with the 18" tire being 45 series and the 19" being 40 series. Both look to be classified as Grand Touring. My guess is that the Uncovered Aeros still win at all but high speeds. Of course without a Mythbusters budget, we'll never know. But this forum is built on speculation!