Do Bigger Tires Really Hurt Fuel Mileage?

Taking I look at the math behind tire size if you don’t get your vehicle calibrated to the new size. Most of the time the fuel mileage is not nearly as bad as it seems

Dobinson’s
MotoFab 

[christianpruna]

Good analysis. Appreciate the effort in breaking it down to numerical level.

[Bsims]

You are not wrong but you are not correct either. You are only looking at one small variable when it comes to losing mpgs with a larger tire size. The thing that will kill majority of mpgs in a vehicle is tire weight, contact patch, and tread type. Let's say the 31" Tire you are talking about is a factory wheel and tire setup that is weighing in around 65lbs. When going to a aftermarket wheel and tire you are most likely going to be between 100-120lbs. With almost doubling the rotational mass your vehicle is going to have to work way harder to get to and maintain the desired speed. Second is the area of the tire that is contacting the ground or "contact patch". A 31" tire is most likely going to be either a 265 or 275mm wide tire. When moving up to a 33" or 35" tire it is most likely going to be a 12.5" wide tire. The 12.5" wide tire has a much larger contact patch with the road thus creating more friction, which will lead to your vehicle needing to use more energy to rotate the tires. Lastly is tread type. I am assuming that the factory 31" tires are going to be a highway tread patter which is designed to be one of the smoothest surfaces between tire and pavement. If you take a 35" tire with a mud or even hybrid terrain tread pattern with large nobs, it's contact to the pavement will not be very smooth as you will have large gaps between the nobs which will most likely cause the tire to lose rotational energy. This would cause your engine to pick up the slack and cause you to burn more fuel. So again you are only looking at a very tiny/miniscule factor into losing mpgs by going up tire sizes when there are many factors. Even wind resistance is a factor as well. I have gone from a factory 265/70/17 tire to a 35x12.5x20 all terrain, with that I went from 26mpg to roughly 17mpg. And yes I have already calibrated my speedometer and used hand calculation on both tires. I assure you that you will be losing a hell of a lot more then 2mpgs when Going up in tire size if you do not calculate all of the other factors.

[videoshomepage]

Just drive a known distance with a known amount of fuel in the tank. Replace the burnt fuel and do the math for mpg. You're correct in that you can't trust the vehicle's computer.

[duke]

If you run big tires on 1ton dually, you have a factory option on gear ratio, selecting a 4.10 with 37 inch tires actually gets better mpg than stock 3.73 with stock tires. It has to do with rpm range at cruising speeds

[coyote]

Great vid and something I have known since 1998 when working at a tire shop. But back then, just as I still do today, I / we figured out fuel mileage by miles driven divided by fuel put back in at fill up.
In my current case, on much smaller tires on my little 4 banger 2WD trucklet, I went from a 225/70R15 (27.4") to a 30x9.50x15 witch made a roughly 9.5% difference. My truck got a very consistent 23 mpg on the stock 27's. So for example on my last refill yesterday I had driven (by the odometer) 254 miles, I put in 13 gallons, so that showes 19.5 THEN add in the 9.5% discrepancy, the real true MPG was 21.4.
So, yes, I use more fuel. True. But not from 23 to 19.5 if someone does not compensate for larger tire size. Formula for a 9.5% larger tire actual fuel mileage: Miles driven ÷ gallons used X 1.095=

[mvmedved]

if you change your tires and travel 8 miles but your computer thinks you traveled 7 miles with 20 mpg then your actual mpg is 22.86 mpg.

[XxTournaquetxX]

This makes complete sense. I went from a 32 inch highway tire to a 33 inch AT tire, the AT tires were only 2 pounds heavier so 8 pounds total. I was averaging 20mpg and now my dash says I average 18.5. I knew I couldn't have lost that much mpg from a single inch.

[jameswag]

Math is the 🔑. Another give away is in the amount that your speedometer is wrong. On my 33’s my speedometer reads 3.5mph under the actual speed. 3.5/60=.05833 or almost 6%. If I was a betting man I would say that a GX with 35’s speedometer would read 7 mph under actual speed. Great video!

[RimaxiRuck]

My truck on stock tires 20s 275 65 were getting 22-24mpg @78 mph i went after market to 22s 35x12.5 and now i get 15mpg so yes it does affect a lot remember the bigger the wheel and rires the more weight and the more torque you lose on the pavement

[warrenlucier]

Aside from the weight gain the differential in the tire circumference changes the final drive ratio. It's been years ago, but a friend of mine install 37.5 " tires on his Dodge Power Wagon and wondered why he kept having driveshaft problems. I enlightened him that the 3.55's weren't the same, due to tire circumference and installed 4.88's (torque multiplication) into both differentials; problem solved. This would go for figuring the vehicles fuel mileage also.

[sgoldste]

Interesting topic, Ryan. Do you know how to recalibrate the computer to adjust for tire size?

[dennismudd]

I want bigger tires.. but everytime I read these comments. I'm like maybe I should stay where I'm at.. lol

[ffstop]

You are stating it is a calculator for difference in tire weight. On another website when in reality it is tire size and weight. You could find a larger tire that weighs the same or less and you calculations will be off. Since the tire is unsprung weight you have to take into account the rotational mass that is now heavier, requiring more torque to turn the heavier wheel. More torque output equates to lower mpg (by how much depends on how heavier the new tire) and after hitting cruising speed how much HP to maintain.
Plus a larger rotation component will require more force to stop.
More factors than just the little cheat sheet.

[andreasgartland]

If you go up one size and use highway tires, do not apply the pedal as if you are in a cartoon, you will see better fuel economy. BTW, do the same math with new tires and the same tires on the warning tab, Free tip, if you only buy used tires - then buy the one size bigger because the height is practically the same.

[mikejoeinc.]

Thank you, i was getting worried . i just install the 2-in lift kit and got the bigger size tires and the amount of mileage that I was getting after calculating i was thinking that I messed up,

[oscarbear]

Basically if I had a giant wheel, with 4000inch wheels, I would Basically not get any mileage on my car

[mizer]

Your math is interesting but not completely accurate. Less tire revolution is not the only problem. U also have to account for weight difference, bc now the engine have to work harder

[cricketsamsunga]

What a waste of life
It's a yes or no question and you told us nothing.