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[William H. Gatez]

2002 sentra - replaced the stock bridgestone potenza re-92s, which had
71,000 miles on them, with goodyear american eagle h2's. mileage immediately
went from a consistant 38 mpg to about 35. new tires are properly inflated,
balanced, and are of the same size (195-60r15).

can different tires really make that much difference? nothing else has
changed with the car.

[SteveB]

Auto Express magazine (U.K.) tests tyres every year and among the tests is
rolling resistance. I've seen RR figures from around 70% with the worst
tyre to 100% relatively speaking with the top performing tyre, and 6%
difference is reckoned to be worth 1% in fuel consumption, so 30% drop would
be about 5% or about 2mpg in your case. Funny enough, I seem to remember
Goodyear being the worst.

[Ulysses]

I replaced the General brand tires that came on my '04 Frontier with
Michelin LTX M/X tires and the gas mileage went down from 26 to about 24.
The new tires are slightly larger in diameter than the originals so they are
not rotating quite as many times during the commute but the amount of
gasoline required to fill the tank is more than it was.

[Jerry G.]

As your tires wear, the diameter is decreased slightly. Over a long
distance, there can be a small percentage difference in the odometer
accuracy. Also, the old tires had less thread, thus had less road grip.
With more road grip, there will be a little more roll resistance, and
thus slightly less fuel economy.

Jerry G.

[Andy Champ]

I'm afraid I disagree.

The rolling diameter might affect the distance travelled per rev, and
thus make the odometer read differently. However I think this is maybe
1/4 inch in perhaps 10inch radius of the wheel - 2.5%. Not easy to
spot, maybe 1 mpg.

Less grip on the road would mean you would be wasting energy at the
road-tyre interface, which is energy that must come from your fuel. Bad
news, and not conducive to good economy. In practice you spend almost
all your time with adequate grip for the way you are currently driving,
and I don't think it'll matter at all.

I think rolling resistance is mostly about bending the rubber of the
tyre, and not about grip at all.

Andy

[Jason]

Rolling resistance takes into account the material the tire is made from,
inflation pressure(underinflation will increase resistance because more of
the tire is in contact with the road, thus decreasing mpg), and the tread
pattern. There are others of lesser importance, but of these three the
inflation pressure is the most important because of the direct relation to
mpg.