OOOOOPPPPS, my mistake forget the above post. Jeeeesssee, I hate it when I SCREW up!!!

 

I think that I may reword that quote above to "My son tends to make a lot of short bursts, around town trips" given the 10 mile difference

I think that he likes the acceleration!

 

OK Dougs, now I understanding what you're saying about summer vs all-season tires, but even though they are listed as the same size, in reality they really aren't.
That's because you're talking about Michelins vs Continentials, and there will always be a different hight, or width to contend with simply because there is no "Industry standards" that dictate that tires have to meet any exact specifications, for comparable sizes.
Bladecutter, you're absolutely correct about the tires weight effecting the gas mileage. But I would think that would be more noticable in stop and go traffic instead of on the highway. A heavier tire would cause the engine to use more gasoline just to get it moving than a lighter tire would. But on the highway at a constant speed, the heavier tire may actually improve the MPG thanks to a "flywheel" effect, creating more inertia.

 

How can a tire that sticks to the road do more revs in a mile as opposed to a tire that does not stick to the road? Surely if a tire does not stick it has to be slipping, therefore more slipping means more revs per mile.

Revs per mile, with no slip is a mile divided by the circumference of the tire at a certain tire pressure and that would be the figure the tire manufacturer would publish. Unless they add some correction for changes due to vehicle weight and I doubt that.