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Do Larger Tires Get Better Gas Mileage?

by The Happy Rock on September 9, 2008

Frugal science question of the day.

Do larger tires equate to better gas mileage?

Discuss.  Let’s pull out our 8th grade physics and see what we come up with.

{ 11 comments… read them below or add one }

Glory September 9, 2008 at 4:24 am

I am not quite sure but I think the do. Does anybody know for sure??/

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The First Creditor September 9, 2008 at 7:20 am

I can’t really say from a sound physics point of view, however the first thing that comes to mind is that the larger wheel will weigh more, and yield worse gas mileage.

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John September 9, 2008 at 4:48 pm

As any good cyclist will recognize, the most important things to worry about when reducing weight and increasing efficiency are the parts of the bike that spin. Very light tires that are inflated to the maximum create the greatest efficiency for the cyclist. I’m sure it applies the same to vehicle gas mileage as well – so I guess I agree with The First Creditor that heavier wheels are not good for gas mileage.

An interesting variant (and maybe this was the original question) is: if you have two tires with the same mass where one has a larger diameter than the other – which one, if any, provides better gas mileage?

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KirkRoy September 9, 2008 at 6:48 pm

I’m no physicist or engineer… The weight issue (unsprung weight) may depend on type of driving. For constant speed/highway driving the flywheel effect of a heavier wheel may be beneficial (same goes for cycling as well). For stop and go, where you must accelerate from a stop or from low speed, lighter wheels ought to do better (also applies to cycling).

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The Happy Rock September 9, 2008 at 11:16 pm

What about diameter of the wheel like John said. One revolution of a larger tire will take you further than smaller tire.

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Bill September 10, 2008 at 1:42 pm

All other things equal, larger rolling radius (i.e., bigger wheels and tires) equals better gas mileage. But it may be very insignificant.

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Michael December 11, 2008 at 11:05 am

It won’t really matter. At highway speeds the fuel economy of a vehicle is dictated by wind resistance alone (the terms regarding this in the governing fluid mechanics equations are non-linear and increase rapidly). At low speeds the fuel economy is dictated by numerous things, including the friction of bearings & pistons in the engine, friction between gears in the transmission, friction in the differential gears, friction between the tires and the pavement, and probably many others. The force required to push a vehicle down the road comes from the torque from the engine. Torque is force*leaver arm, so to get the same force with an increased leaver arm (i.e. increased tire radius) would require an increase in torque. That requires a higher RPM, and probably a higher fuel consumption rate.

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The Happy Rock December 11, 2008 at 9:19 pm

@Michael – Thanks for the comment loaded with info.

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Ridgway April 12, 2010 at 5:21 pm

I had to test the theory of the bigger tire equals better gas mileage to actual know what happens. The idea is tempting because a longer circumference per revolution should give better mileage. And, I had thought I had tested the mileage accurately with the tires that came with the Geo Tracker which were bald 235/75R15. From Denver to Grand Junction is 250 miles and I did the drive with fuel still showing on the gage and I calculated 29 MPG. I purchased new tires in the size the car was designed for, 205/75R15 but in a Uniroyal Liberators A/T (a heavy tire). In subsequent trips I was only getting 24 MPG. I concluded that the bigger tire was the better with mileage. Therefore, I took the 205s off and put on 235/75R15 in the same make and model tires (even heavier tires). I ran the same trip again and to my horror found I had to fill up before reaching my destination, achieving only 21 MPG.
I can conclude absolutely that the 235 got worse mileage that the 205 over exactly the same road, temp and conditions.
What happened on my first test with the bald tires? They were extremely light due to their build and the fact that they had no tread left made them even lighter. And/or, I could have made a mistake in the calculation although I did it twice – always a possibility.
The one thing I do know is that given the same car, same conditions, same road etc. the designated size tire worked better that the oversized tire size. This is a test you can experience viscerally and as you feel the engine struggling to push the heavier tires up a hill you will know why it hurts mileage. It is like a crow bar being lifted by a balloon or a lead ball rolling up hill – bigger isn’t better.
This is a test you may find expensive to try. I got lucky and didn’t loose all my money.

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found this April 28, 2010 at 2:35 pm

Tires and tire pressure have a great deal to do with your car’s gas mileage. If you put a lot of miles on your car, consider swapping the car’s tires and wheels so that you end up with tall, narrow tires that have a high pressure rating. This may easily cost you $500 or $600 but could make your gas mileage jump from 18 mpg to 22 mpg. A couple of added benefits are that skinny tires are generally better in the rain and on snow, and tall skinny tires give the car a softer ride. That’s usually a good thing for highway cruising.

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mike May 6, 2012 at 11:09 pm

i used to have 185/65/r15 and at 110km/hr i got exactly 6.5 L/100KM (36mpg) now i run 215/70/r15 ,over all the tire was about 3 inches bigger in diameter, speedo is off by 11.5%, at the same speed of 110km/hr ,and after math to calibrate speedo, i now get 5L/100KM(47mpg). in the city i don’t notice much difference tho, it sits about 8L/100km(29mpg).
i do a lot of highway ,so this was a good thing. but in city it stays the same.
hope this helps

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