Larger tires decrease gas mileage?

timn1984

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Ok I know this has been talked about before but I cannot find it anywhere. Is it just my imagination or has my gas mileage gotten that bad. I went from stock Wrangler 255/65/18 to BFG 275/70/18. I was getting between 20-22 on the road and about 17-18 in the city. Now I seem to be getting 18 on the road and 16 in the city. Are these real numbers or is it the large tires causing problems with the MPG calculations?





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conFUcius

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Ok I know this has been talked about before but I cannot find it anywhere. Is it just my imagination or has my gas mileage gotten that bad. I went from stock Wrangler 255/65/18 to BFG 275/70/18. I was getting between 20-22 on the road and about 17-18 in the city. Now I seem to be getting 18 on the road and 16 in the city. Are these real numbers or is it the large tires causing problems with the MPG calculations?
Did you recalibrate for new tire size using a programmer (e.g. Flashcal, Tazer)? Depending on the terrain and speed at which you drive, you may be lugging the engine without a re-gear which would waste more gas too.
 

Chupacabra

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If you don't recalibrate due to larger tire, your odometer miles will be less than actual miles which will affect your calculated MPG too. Your speedometer will also read slow.
 

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You should expect to lose 1-2mpg when upsizing tires. It's tough to call because there are a lot of factors. Tire size changes your final drive, and larger tires are obviously heavier which contributes to rotating mass, and that has by far the largest effect on efficiency when compared to other mods. Also, as mentioned, you need to make sure the vehicle is aware of the tire size it's riding on or else the MPG number it calculates will not be accurate.
 

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recalibrate speedo and re-test
 
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timn1984

timn1984

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Did you recalibrate for new tire size using a programmer (e.g. Flashcal, Tazer)? Depending on the terrain and speed at which you drive, you may be lugging the engine without a re-gear which would waste more gas too.
Whats the best Flashcal or Tazer?
 

conFUcius

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Whats the best Flashcal or Tazer?
A lot of people like the Tazer and it offers a lot more features. If you don’t plan on using a bunch of those features, consider a Flashcal.

A lot of people who go from a JK to a JL may look to offload an unmarried/unpaired (they are VIN locked). Just need to buy the gateway bypass module for like ~$50.

https://superchips.com/shop/gateway-bypass-module-299

Since I had my Flashcal I unpaired from my JKU, I just picked the module to use to re-calibrate.
 

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Heavier tires decrease mpg, those are unsprung rolling weights.

If you can find a larger tire but lighter, you can increase mpg.
 

oldcjguy

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Like others have said, make sure you recalibrated your speedo. For every revolution of the a tire, a taller tire travels a longer distance. The jeep computer can only know how many rotations a wheel made. You have to tell it how tall your wheel is and it will calculate the rest. Stock calibration with a taller tire you are actually going further than your odometer reports. You're also going faster than your speedo reports too. That will throw off your mpg calculations.
 

Oncorhynchus

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I’m getting 17.5 mpg hwy on 35/12.5/17 with stock 3.45 gear ratio on my Sahara powered by the V6 Pentastar.

You can take a longish drive on flat freeway and do the manual calculation with Google maps and tank fill gallons.
 
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The weight of the larger tires will make the most impact on your mileage. I've found anywhere from 1-4 mpg loss depending on tire size and weight, and vehicle drivetrain.
 

DrRay81

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I'm getting 24.5 city and 27.2 highway on 37" ridge grapplers............but I have a diesel, before the lift I was getting about 26/28
 
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timn1984

timn1984

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Just ordered the Tazer Mini
 

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I'm getting 24.5 city and 27.2 highway on 37" ridge grapplers............but I have a diesel, before the lift I was getting about 26/28
That's impressive because those tires heavy AF. I'm actually swapping from Trail Grapplers/Beadlocks to an AT/stock wheel (w/spacers) for winter driving -- losing 40 pounds per corner (37" KO2, about 1/4" smaller than the Nittos). I'll likely trade mine for a diesel at some point. Hopefully a dual battery solution will come out.
 

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Most vehicles overestimate their gas mileage. I’ve read that SUV’s typically show they got about 10% better mpg than they really do and I can verify that pretty close. I use an app called Fuelly (free version) and its way more accurate. Every time I fill up I log the odometer reading, amount of gas to fill up, and the price per gallon. It keeps your history and graphs trends. I can’t fill up without it now.
 

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