[mikem]

I'm not saying it's not possible but scan tools really can not be trusted to be accurate. Both my friend and I carefully watch our scan tools live readout and do everything possible for the best mpg. I'll even stay in the slow lane with cruise at 60mph for long stretches. He's a honda tech and I'm an amateur but our results have been pretty consistent.

I think the biggest disadvantage to larger rims is the increase rolling resistance. My high quality 17's, although light, are very wide. I think total unsprung weight is pounds less with stock rims/rubber also. This car is scary fast around corners when lowered with big tires!

EDIT: I also wanted to add that my corolla had 185/65-14 in it's stock configuration and then they were downgraded to 175/65-14's. No noticable effect on fuel efficiency but the car did feel less capable during cornering and acceleration.