[comptiger5000]

Larger tires are less disturbed by small imperfections in the road, which makes sense for lower real-world rolling resistance. That, and taller effective gearing, combined with off-road use are why I upgraded my Jeep from the stock 225/70R16 tires to 245/70R16.

It had no noticeable effect around town (not a lot of extra weight, and taller effective gearing), and a fraction of an mpg gain on the highway at 60mph. The instant mpg on the overhead display reads the same as before most of the time (better RR, but worse aero), but when climbing steeper hills, it typically stays about 1mpg higher than it used to due to the taller effective gearing.

The effects will, however, vary from vehicle to vehicle. In my case, I think the primary reason I saw gains was due to the Jeep needing taller gearing on the highway (with current 3.73 axle gears and larger tires, it turns 1750 at 60mph and climbs any hill without downshifting).