Tire size vs gas mileage

[jaxsage]

My stock ranger is sitting on lt245 75/r16's. I was thinking of upgrading to 265 75/r16 with new wheels with some more backspacing. My question is how much will those tires lower my mpg. I want the bigger tires but I don't want to sacrafice any mpg because I am already down around 14-17.

Thanks for any help

 

[99RangerKrazy]

As tire size goes up, gas mileage goes down. You're only going to go up an inch or two, it'll probably drop some but not a huge amount. But if you're too worried about gas mileage, I would leave them stock.

 

[JeepRecoveryTeam]

I run 38s and i get about 0 miles per gallon.. cuz it just sits in the garage its a trailer queen. anyway you might not even notice a difference in mpg but you might be able to notice a sight change in acceleration but not much. get a 15inch wheel look way better

 

[Rifleman]

The wider stance will hurt worse than the ~inch difference in height. Once you start getting the tops of the tires out from behind the bumper and under the fenders any at all you dramatically increase wind resistance. Weight of the rolling assembly is something to look at as well. Going from the aluminum stockers to a steel aftermarket will increase the weight of the rolling assembly and decrease both acceleration and braking ability.

 

[Original_Ranger84]

I didn't notice a big drop when i went from 235's to 31's on my 99 or my 84. Probably around 1-3mpgs, a 4.0L probably will have like 1-2 if you go a little bigger it also depends on the tread design and load range if you won't really be doing much off roading i would see if you can get a standard load cause they are way lighter.

 

[Rifleman]

I didn't notice a big drop when i went from 235's to 31's on my 99 or my 84. Probably around 1-3mpgs.

That is 20 to 60 miles off a tank of fuel. The minimum of which is a round trip to work and back one day. I'd call that a fairly big drop.

 

[dogboy]

When I went from stock 235/75/15's to 33x12.5x15's, my in town mileage went down from 16 or so down to about 14, but my highway went UP from about 17, to around 19.

With where I drive (mix of city and highway) my mileage actually stayed about the same overall.

The wider stance will hurt worse than the ~inch difference in height. Once you start getting the tops of the tires out from behind the bumper and under the fenders any at all you dramatically increase wind resistance. Weight of the rolling assembly is something to look at as well. Going from the aluminum stockers to a steel aftermarket will increase the weight of the rolling assembly and decrease both acceleration and braking ability.

I am definitely going to have to disagree with you on that! My tires stick out slightly past the fender flares, yet my mileage went UP on the highway (the engine turns few revs for the same speed, therefor, to a point, you get better mileage, assuming you are not bogging the engine). That is the opposite of what would happen according to you. According to you, the mileage should have gone down, which it only did in the city, which has very little air drag (25-35mph).
I bet if you put on 3" wheel spacers (yes it would be stupid) on stock wheels and tires, your mileage would stay virtually the same. But if you put really tally tires that stuck out the same amount as stock wheels/ tires, I bet you're mileage would go down in the city, and up on the highway (like mine did).

 

[Rifleman]

Your results are interesting.

Although I also disagree on your theory of the spacers with the stock wheels. Idiot ricers that can't afford the oversized rims do that all the time and complain about killing their fuel economy because they can't afford gas either (all the while it never effects their driving their POS honda like they're in a 24/7 drag race).

The effects on a truck aren't as noticable as a car because the aerodynamic efficency of a truck is only slightly better than a concrete block to begin with, but the fact remains any time you increase the front facing profile (lifting or widening), you increase wind resistance. There are many things to take into consideration and I would venture to say that your benefits (increased distance per rotation, rim and tire weight, rolling resistance variances from the tread patterns, air pressure, or sidewall firmness, as well as the gearing a.k.a. the RPM range you went from and to relative to your truck's power band) simply outweighed the drawbacks on the highway. The physics of it don't change vehicle to vehicle.

Don't forget that if you do not correct your Speedo readings when you change the tire size, the odometer reads incorrectly as well (and goes farther off the faster you go just like the speedo) and you lose the ability to accurately calculate the MPG differences.

 

[Original_Ranger84]

Don't forget that if you do not correct your Speedo readings when you change the tire size, the odometer reads incorrectly as well (and goes farther off the faster you go just like the speedo) and you lose the ability to accurately calculate the MPG differences.

Well i guess i noticed a bit more of a drop cause i got 3 major hills between me and town that i drive 20 miles a day round trip... the hills really kill me. I just got back from a trip and got around 22MPG (31's) vs 20MPG (235's) 200miles and fairly flat. I also didn't lift the truck or anything and all air at 35.

also my 84 never liked winter and stuff so the 2mpg off from that kinda doesn't count, from 245's to 265's i would expect a 1mpg drop max unless you get like a load e tire then it would be way more.

 

[strvger]

well, mine went up. went from 205/75x15 to 215/85x16 on my Geo Tracker. it has 5.13 gears and the ratio changed enough to get me about 3mpg more. the trick is my taller tires (about 31 in. vs. 27 in stock) are also still narrow enough to keep tucked into the original wheel wells. yes, it is lifted to fit them easily without rubbing, but the main thing again is: taller tires changed the effective gear ratio and keeping them narrow didn't increase the drag. can work if you're careful. original mileage was 28mpg, current is just over 31 mpg.