# Tire size vs mpg?



## Teksyn (Aug 20, 2005)

It's time to get new tires for my 2013 F150 Screw 4x4 with 2" level kit. I'm think of going from stock 275/55/20 (32") to a 275/65/20 (34"). Does anyone know about how much I should expect to lose as far as mpg?


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## Sgrem (Oct 5, 2005)

2mpg 
You will feel a difference in power which will make you use more pedal. And at your highway speed your engine will have to work harder for same rpms will be higher for the same speed and work load.


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## goodwood (Mar 30, 2009)

About 2 mpg is right. Had 2004 F150 with a 5.4 CCSB 4x4. May lose less or more depending on your gearing and engine.


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## acoastalbender (Jul 16, 2011)

Just by the numbers it doesn't seem that you would lose mileage.....the 34's have over 6in greater circumference than the 32's. At that size the 32's would turn 630.57 times in a mile while the 34's would turn just 593.36 times, a difference equating to 331.1 ft.or over 6%...the engine has to turn over more times to make a mile with smaller tires than it does with bigger tires. So how do you lose gas mileage by going to bigger tires...?....jm.02

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## baystlth22 (Aug 12, 2008)

acoastalbender said:


> Just by the numbers it doesn't seem that you would lose mileage.....the 34's have over 6in greater circumference than the 32's. At that size the 32's would turn 630.57 times in a mile while the 34's would turn just 593.36 times, a difference equating to 331.1 ft.or over 6%...the engine has to turn over more times to make a mile with smaller tires than it does with bigger tires. So how do you lose gas mileage by going to bigger tires...?....jm.02
> 
> .


You are correct, engine RPM's will be lower at road speed. May not even notice a difference in town unless you have a lead foot.


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## Sgrem (Oct 5, 2005)

It's the physical weight of the tires that affect mpg the most. Engine has to work harder to turn em.


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## calphil (Jan 17, 2011)

I have 34" on my 13 .. But programmed and cold air .. I run about 14 in town and 17 on highway hand calculator 


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## Gottagofishin (Dec 17, 2005)

sgrem said:


> It's the physical weight of the tires that affect mpg the most. Engine has to work harder to turn em.


This. Plus lifting and leveling affects the aerodynamics and creates drag. My stock F150 4x4 screw gets a little over 17 in mixed driving.

Most people with moded versions of my truck get 2 to 3 mpg less than me.

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## Pocketfisherman (May 30, 2005)

Wider tire has a bigger contact patch, a lot wider strip of rubber that has to flex and bend which gives a bigger tire more rolling resistance. That in turn requires more power to turn the tire over and more fuel. Wider tires have more frontal area and add more drag to the vehicle. Wider tires often move crusing speed RPM out of the peak torque sweet spot where the motor is most efficient.


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## loco4fishn (May 17, 2010)

*This*



Pocketfisherman said:


> Wider tire has a bigger contact patch, a lot wider strip of rubber that has to flex and bend which gives a bigger tire more rolling resistance. That in turn requires more power to turn the tire over and more fuel. Wider tires have more frontal area and add more drag to the vehicle. Wider tires often move crusing speed RPM out of the peak torque sweet spot where the motor is most efficient.


Bingo!


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## acoastalbender (Jul 16, 2011)

All the above being correct or plausible, I wonder how many people recalibrate their speedometers after going up in tire size....or compensate for the error. In the example I used above you would need at least 6% more mileage added before dividing by fuel used...it would also be a good idea to know your actual highway speed as the error is a constantly increasing one and changes with speed....

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## TexasFlatsFisher (May 7, 2010)

Pocketfisherman said:


> Wider tire has a bigger contact patch, a lot wider strip of rubber that has to flex and bend which gives a bigger tire more rolling resistance. That in turn requires more power to turn the tire over and more fuel. Wider tires have more frontal area and add more drag to the vehicle. Wider tires often move crusing speed RPM out of the peak torque sweet spot where the motor is most efficient.


Bingo x2. The surface area in contact with the pavement has a much bigger affect on MPG than actual tire height. At least when your making a small change from 32" to 34".


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## juan valdez (Jun 21, 2014)

acoastalbender said:


> All the above being correct or plausible, I wonder how many people recalibrate their speedometers after going up in tire size....or compensate for the error. In the example I used above you would need at least 6% more mileage added before dividing by fuel used...it would also be a good idea to know your actual highway speed as the error is a constantly increasing one and changes with speed....
> 
> .


Can't speak for op but in my last truck I lost 1.5 mpg. Worked out to roughly 10%. Didn't re cal speedo but factored in tire difference manually when computing mileage. 
Weight combined with tire patch and aero drag have quite the affect. If op keeps same wheel, it might be less of a loss as usually aftermarket wheels are heavier than oem


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