i have a 03 6speed and i put 18x8s on which i think may have made my MPG worse and my car a bit slower, though i love the look and handling improvements. Though they weigh the same as stock, the weight is out farther making them more work to rotate. I was pokin around the tire rack and was wondering how much of a difference it would be if i went back to 17s that weight like 15 lbs in regards to MPG and acceleration? Thank You for input

 

From what I gather, every 1 lb. difference in weight for a wheel/tire combination has a differential in unsprung weight of 8 lbs. to the vehicle.

So for example, if a wheel/tire combination were 5 lbs. heavier that would make a difference of approximately 40 lbs. per wheel or 160 lbs. in total to the unsprung weight of the car.

Similarly a difference of 10 lbs. per wheel would double that or be 320 lbs., which would affect acceleration and fuel economy to some extent.

I suspect one of the reasons I get better fuel economy than most of the 4th Gen members on the .org is because I am still running 15" sawblades, with reasonably lightweight Yokohama Avid H4S tires (plus my car is a 5-speed and doesn't have as much emission-control equipment as newer 4th Gens).