Tire size 185 or 195

[Dorkinheimer]

When I bought my 2006 Corolla, my model came with the 18565R15 tires, and more expensive models came with the 19565R15 tires. I was wondering which is easier on gas?

Next summer if I don't change car, I might buy new all seaons, so I was wondering if I should buy the same size 185, or go to the bigger option 195 wide.

I also have winter tires, 195 wide, and it seems to me that going up a hill, the car seems to go from 4th to 3rd as if the car needs more power to go up the hill, while with the smaller tires, it didn't do that as much, which leads me to believe that the 185 wide would be a little easier on gas.

There is maybe a 2.1% difference in circumference.

http://www.miata.net/garage/tirecalc.html

[jkjk15]

I would imagine negligible effects on gas between the 2.

[Dorkinheimer]

I was surprised to see that the bigger tire was cheaper, probably because they sell more.

[JasonA]

As far as diameter, I think the difference is really negligible. The 185/65R15s are a hair shorter, which increases the engine speed given the same gear ratios (and the gear ratios are the same). From that standpoint, the potential to use more fuel is there. But they're also a hair lighter, meaning less rotational mass, which is better for fuel use. In addition, because the 185s are a hair narrower than the 195s, they should produce a hair less rolling resistance, which should also help to reduce fuel use.

But all those factors are likely negligible. It may be worth noting, though, that the Prius uses the smaller of the two sizes. Toyota likely had to make a decision between two very similar sizes (185/65 and 195/65) and for whatever reason, they chose the smaller size for that car (even though it's relatively heavy for its size, and the larger tire would have made a better choice from the weight-carrying standpoint).

Bottom line: I think that, ultimately, the 185/65R15s are the most economical choice, but whether or not you'd be able to measure that...I doubt it.

[JasonA]

I should add, your actual choice in tire make/model will have MUCH more of an influence on rolling resistance and fuel economy than the size will. There are some pretty lousy tires in terms of rolling resistance.

[PhatRoyale]

stick with the stock size.

if you're concerned about gas mileage, then buy some low-rolling resistance touring tires.