It isn't quite as clear on my car, where the old Cooper's which were on it when purchased used were not the stock size, so there is a diameter change to take into account. However, it looks like after correcting for that the Defender's took off 1-3 MPG more. Certainly not 8. Other than the loss of MPG I have been happy with the Michelin tires. Michelin rates the Defenders as low rolling resistance tires. There is sadly no good metric available for comparing tires in that regard.

 

Practically no rolling radius change at all.

Michelin makes a great tire. They rode well (likely better than the low rolling resistance tires). Generally I suspect we are not to the point where we can have it all from a tire technology standpoint. There is not a tire that will last 100,000 miles, run at 150+ MPH all day, boost fuel mileage, and achieve 1+ G on the skid pad.