Tire size vs. gas mileage

scrape

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Jul 27, 2008, 10:10:45 PM7/27/08

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I've seen both sides of this argument, but am interested in what
folks here might have to say on the topic. I've got a 2003
Silverado. Stock tire size is 245/75/16. If I go to a 265/75/16,
the tire diameter increases by about an inch giving me about 3%
less revolutions per mile. On the surface, this would give me 3%
more mileage - BUT - how does the increased friction from the
additional tire width and the theoretical increased work the
engine must do play into the equation?

2nd scenario: I can go to a 265/70/16 and have virtually the same
diameter with 20mm more width. How would this factor alone affect
mileage?

JR

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Jul 29, 2008, 1:50:46 AM7/29/08

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I think you would have to do some pretty tight measuring to really see a
difference in your mileage.
It would LOOK a lot nicer with the bigger tires. I did it to my 97 Yukon and
was pleased with the new
look, and they didn't rub anyplace.
Regards,
JR

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Rick Cooper

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Jul 30, 2008, 1:12:37 AM7/30/08

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tire size has nothing to do with gas mileage

scrape

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Jul 29, 2008, 10:45:15 PM7/29/08

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On Tue, 29 Jul 2008 22:12:37 -0700, "Rick Cooper"
<gla...@telus.spam.net> wrote:

>tire size has nothing to do with gas mileage

How can it not? If a tire has a (extreme example) 30% larger
diameter, it's going to travel further given the same amount of
engine RPMs. At some point there has to be diminishing returns
due to more effort being required. My question has to do with
where that point is reached.

Rick Cooper

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Jul 30, 2008, 3:18:00 PM7/30/08

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"scrape" <scrapeN...@earthlink.net> wrote in message > How can it not?

basic physics.........you could run bicycle tires (if it were possible for
them to support the vehicle weight) and the vehicle would get the same gas
mileage

Craig M

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Jul 30, 2008, 12:32:18 PM7/30/08

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I think you need to re-think that, if you loose 5 pounds of air in your
tires, you make the tire smaller, and thus will make your milage go down.
What changing tire sizes does, it will make your speedomter off, so you may
get a ticket, now that will cost you some money.
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Rick Cooper

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Jul 30, 2008, 3:50:15 PM7/30/08

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"Craig M" <craig...@sbcglobal.net> wrote in message
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> I think you need to re-think that, if you loose 5 pounds of air in your
> tires, you make the tire smaller, and thus will make your milage go down.

Yeah, but I wasn't talking about "drag". I was talking about tire size.

Steve

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Jul 30, 2008, 2:03:37 PM7/30/08

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A larger diameter tire has the effect of reducing the effective rear-end
ratio. There is a well-known relationship between rear-end ratio and
gas mileage. I expect that a 3% change in rear-end ratio would have a
small impact on gas mileage - and a 3% change in tire diameter should
have the same impact.

--Steve

scrape

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Jul 30, 2008, 6:31:33 PM7/30/08

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I think you're assuming that the engine is doing the same work and
this may be the case if the final gearing is changed to give the
same ratio based on a different diameter tire, but a larger tire
is going to go further given the same number of engine
revolutions. The engine may burn the same amount of fuel running
at 2500 RPMs for one hour regardless of tire size, but the vehicle
would have traveled a greater distance. MPG would increase.

Basic math.

scrape

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Jul 30, 2008, 6:32:28 PM7/30/08

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Would, however a slightly fatter tire negate that difference due
to additional drag?

There has to be a "sweet spot" somewhere.

Steve W.

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Jul 30, 2008, 8:30:38 PM7/30/08

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Only if the tire was the same diameter as the old one. Also the
thinner tire would get better mileage due to the reduction in surface
friction. Has been proven many times.

It is FAR more than basic physics.

--
Steve W.
Near Cooperstown, New York

Stormin Mormon

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Aug 21, 2008, 6:30:46 PM8/21/08

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Size matters. Especially to woman drivers.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
.

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Stormin Mormon

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Aug 21, 2008, 6:30:22 PM8/21/08

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about 30 miles west of Cleveland is that point.

More seriously, I don't know.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
.

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None4You

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Aug 22, 2008, 3:59:47 AM8/22/08

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"Stormin Mormon" <cayoung61**spamblock##@hotmail.com> wrote in message
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I was under the impression for a long time that taller, skinnier tires
offered better gas mileage. Due too less rolling resistance , as the contact
patch is smaller. and less air resistance. And they travel farther for the
same amount of revolutions. They also get better traction in the snow.
And those type of tires ( Old folgy tires) generally have a harder rubber
compound that creates less friction too. Then wider lower aspect sporty
tires. They are also cheaper to buy. That's my story and I,m sticking to
it.

None4You

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Aug 22, 2008, 4:09:19 AM8/22/08

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"Craig M" <craig...@sbcglobal.net> wrote in message
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No it wouldn't. It would get better mileage . The tire would have to be
super hard and the contact patch would be super small. Also air resistance
would be much reduced. But don't try and turn it fast. It will slide .
That's why all high mileage experimental electric, or other vehicles have
skinny tires. Less rolling resistance. Any wider tire will get worse
mileage if everything else stays the same. More road resistance and air
resistance. If you could mount a razor blade ring on a wheel . And it
could support the weight and the road could take it. It would get better
mileage then a bicycle tire.