I switched out my 17s OEM all-season run flats for my summer 19s OEM Pzero performance run flats. Now, I noted a drop in MPG for the last three tanks. I had been getting just above 25 and now I am around 24 mpg (yes it is low and I live in a mountainous area--all hills and curves). I have not changed anything else--same gas, same routes, etc. With less rubber on the 19s the ride is obviously rougher but I read that the larger wheel can lower mpg because of the increased weight. I should add that my mpg increased last fall when I put on the 17s for winter. Have others experience the same with mpg?

 

Heavier tire and wheels will lower your mpg. Stickier tires (more rolling resistance) have some affect as well.

 

Now that I put away my winter tires (205/55-R17) for a set of Michelin Pilots (225/50-R17), my mileage has dropped a couple of miles to 25.5 mpg.

I'm using the same stock wheels for both.

 

Yes, weight of both the wheel and tire play. As does the tread pattern and width.

 

I experienced the same type thing. I went from 15 inch to 17 inch wheels and notice a 3 mpg drop and decreased performance due to the extra weight. I finally settled on light 16 inch wheels .

 

it should be fairly slight depending on the wheel/tire combo, but definitely will

 

Wheels and tires and weight make. Huge difference, my buddy changed his 14s to heavy sticky tire 17s and lost a lot of initial power. The car almost stall off the start because of the increased weight and diameter.

 

Beyond the unsprung weight issue, wouldn't overall diameter affect the calculation like it does with your speedometer?

 

You will get more drag from a wider tyre because of the increase in surface area presented to the air flow. Maybe a touch more friction also from the larger contact area to the road surface. It will be small amount, but there all the same.

Tab

 

Update. I took off my roof bars and my mileage went up to 26.3 mpg average. That's about 1.2 mpg loss so far from switching from 205/55-R17 (stock runflats last summer) to 225/50-R17 (Michelin Pilots).