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Increase Gas Mileage

If I increase the rear tire size from 14 to 15 inch on my rear wheel drive truck will it affect the gas mileage ?

That depends on how you calculate it! If you use your odometer to measure how far you’ve driven - your MPG calculation will be off. Your odometer assumes you have the correct diameter tires installed.

BTW your speedometer will be off too - and the excuse about bigger tires won’t hold up in traffic court!

depends on the type of truck. 4wd? if you have 4wd it could mess up the differential when used in 4wd. any saving on gas would be eliminated by repairs to the transfer case.

but on a regular 2wd truck the increase in tire size will increase mpg. but your speedometer will be off, and you may get tickets.

wont make any diffrence fitting 15" wheels and tyres if you get lower profile tyres ,e.g if you have 195/60/14 tres now,changing to 195/50/15 on your truck would be a similar overall size

Let me try to clarify, the wheel size itself (14 or 15) has nothing to do with mileage. If you change the actual outside diameter of the tire it will effectively change the final gear ratio. If you end up with larger tires it will most likely increase you fuel mileage slightly (don’t expect miracles). As others have said, it will also affect your speedometer and odometer calibration.

Only if the weight changes or the rolling resistance changes.

Just looking at your real question: If I put tyres that have a larger circumference on the rear wheels of my truck will the mileage increase.

Answer: Maybe, maybe decrease. For each situation including driving style, road conditions driving conditions, traffic, loads in the truck etc. there is an ideal gearing. In this case I am counting the ccircumference of the driving wheels.

Assuming you have a 2WD rear wheel drive truck and you are not fully loading it and not driving up mountains etc. Then you likely will gain a little mileage. On the other hand if you are driving overloaded in the mountains, you likely will loose.

In most situations you would gain a small (you might say very small) amount.

And you can’t accurately measure it because your odometer will be affected.

“And you can’t accurately measure it because your odometer will be affected.”

Agreed, but you should check your speedometer/odometer with a GPS or something anyway. Many speedometers read high from the factory anyway. If it’s off by more than a couple of mph, it’s a good idea to have it re-calibrated.

Thanks for the input has a site about tires and wheels that includes a calculator with which you can find a tire & wheel combination that would have mimimal impact on your speedo and odo. If you take that approach you should have no measurable impact on your mileage unless you go to a wider tire, which you can safely assume will have slightly more rolling resistance.

To answer your question, No. Any improvement will be insignificant. You CAN make a noticeable improvement just by changing your driving habits. The two biggest reasons for poor mileage are rapid acceleration and speed over 60mph. Also, anticipate stops and limit your brake use as much as possible. Hot brakes were heated by burning gasoline…

Bigger tires will make it seem that the gas mileage has gone down. Smaller tires make it seem like there is an improvement. You’ll never know for sure. The higher the car or truck, the higher air resistance you get. The air has more leverage. If you use bigger tires or wheels and you notice no difference, you probably improved the gas mileage. Good luck, but there may be better ways.

 "Bigger tires will make it seem that the gas mileage has gone down. Smaller tires make it seem like there is an improvement."

This is just another way of saying you can’t use your odometer to measure mileage because it’s calibrated to the tire size.

Graig had a good idea - use a GPS to measure your mileage.