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Bigger tires, Better gas mileage?

Bigger tires, Better gas mileage?

Postby MSUPKR [OP] » Oct 27 2011, 9:40pm

Would getting a bigger diameter tire help increase fuel economy? I know the physics behind it for every inch your diameter increases your circumference goes up by 3.14" so you could cover more ground each revolution. A bigger tire also has more mass and there for takes more energy to get rolling. What have you guys seen in personal experiences?
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Re: Bigger tires, Better gas mileage?

Postby parrothead » Oct 28 2011, 5:06am

Not gonna happen--just my experience. bigger tires+more aggressive tread=more rolling resistance=worse gas mileage.
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Re: Bigger tires, Better gas mileage?

Postby trout_champ » Oct 28 2011, 6:49am

That’s the way it was my Wrangler so I’m assuming that’d be the way with my new pick up. In my jeep I lost 4 MPG’s when I switched to the Goodyear MTX.

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Re: Bigger tires, Better gas mileage?

Postby SSGBulldawg » Oct 28 2011, 7:40am

like previously stated yes it would make it worse, depending on the tread pattern/width/weight. but yes in general if your doing more in town then youll get alot worse. my brother went from 33's to 35's and got 2 more mpgs, but he drives highway 60 miles a day.
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Re: Bigger tires, Better gas mileage?

Postby EKinMN » Oct 28 2011, 12:27pm

You math is right (using Pi). Theoretically, it should be the same as reducing your gear ratio. If you have a lower ratio, the engine turns less for every revolution of the tires, and you use less fuel....but that's in theory.
In real world, I have never seen an advantage. The weight of the tire makes a big difference. Plus, if you do not recalibrate your speedometer to account for the change, you will never truly know about your mileage.
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Re: Bigger tires, Better gas mileage?

Postby Z15 » Oct 28 2011, 2:56pm

The problem with changing tire sizes is that the PCM does not know you changed tire size and it still operating with the assumption the OEM size are on the vehicle. This can throw off when the transmission up-shifts/downshifts, when over-drive kicks in, when the torque converter locks. This can cause the engine to work harder because it is no longer is operating within the designed torque range that the PCM is programmed with.

Also, when you go bigger, the tires get wider so any economy that might seem possible is negated by the wider tire causing more rolling resistance (pavement friction), drag (pushing air) and more un-sprung weight, all detrimental to fuel economy.

Ideally you would want to get with skinny tires but there is a slim chance any truck owner would do that. :shock:
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Re: Bigger tires, Better gas mileage?

Postby SRMN8R » Oct 28 2011, 3:50pm

It really depends on the type of driving you do, vehicle weight, and more importantly - your gear ratios.

In an old Ford truck I had, I went from a 9.50 to a 10.50 tire and gained 2 mpg. When I went from a 10.50 to an 11.50, I gained another 2 mpg. Adversely, when I went from the 11:50 to 12:50's, I lost 1 mpg.

These numbers were not gathered over the course of a tank of gas each, but over a 10 year period and over 100,000 miles travelled. If I remember correctly, that old truck had 4:30 gears in it, with the 300 ci straight six motor. It was a dream off road with traction lock front and read diffs, but it was way over-geared for the highway.


On my 83 Jeep CJ, I dropped from 18mpg with 11:50's, to 14 mpg's with 14:50/35's.

Lots of variables. YMMV.
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Re: Bigger tires, Better gas mileage?

Postby MSUPKR [OP] » Oct 28 2011, 5:59pm

Z15 wrote:The problem with changing tire sizes is that the PCM does not know you changed tire size and it still operating with the assumption the OEM size are on the vehicle. This can throw off when the transmission up-shifts/downshifts, when over-drive kicks in, when the torque converter locks. This can cause the engine to work harder because it is no longer is operating within the designed torque range that the PCM is programmed with.

Also, when you go bigger, the tires get wider so any economy that might seem possible is negated by the wider tire causing more rolling resistance (pavement friction), drag (pushing air) and more un-sprung weight, all detrimental to fuel economy.

Ideally you would want to get with skinny tires but there is a slim chance any truck owner would do that. :shock:


Z15 thanks this post is very helpful,
I never really thought about that but that leads to another question. Some chips have a setting to flash the computer if you have changed your tire size(Hypertech max energy). Does this just change the speedometer to correct it or actually flash the PCM to correct the shift points?
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