Could tire size difference be killing my MPG? (1 Viewer)

[hodag]

On the wife's 00' 4Runner, I just swapped out the worn 265/70R16 Goodyear Wrangler ATs for a set of 265/75R16 Kumho AT825s. Last fill up, the wife calculated the mileage at 16.5MPG. We had been getting 19 pretty regularly.

I think she is doing the math wrong, or she didnt reset the odo. But do you guys think I would lose 2.5 MPG going from a 265/70 to a 265/75?

Hodag

 

[bkg]

On the wife's 00' 4Runner, I just swapped out the worn 265/70R16 Goodyear Wrangler ATs for a set of 265/75R16 Kumho AT825s. Last fill up, the wife calculated the mileage at 16.5MPG. We had been getting 19 pretty regularly.

I think she is doing the math wrong, or she didnt reset the odo. But do you guys think I would lose 2.5 MPG going from a 265/70 to a 265/75?

Hodag

First of all, the 75s are about 4% larger in circumfrence than the 70's, at least according to the PD of my 4runner. So you need to multiply the 16.5 * 1.04 to get your actual mileage. Bigger tires do affect mileage, though, aside from speedo differences. That said, my 96 gets 19.25 (corrected) cruising at 75-80 w/ 75s, but it's not stock, either.

 

[hodag]

Thanks for the info. My wife is an engineer, so doing some extra math is right up her alley. After I posted, I remembered that I worked on the battery cable between fill ups, so that also may have affected the total mileage.

Thanks for the help, Hodag