New Tires


#1

I need new tires for my Suburban 1500. Currently I have 265 70R16 on. I have talked to several tire dealerships and some of them have told me to go to a 265 75R16 to help increase gas mileage. First of all would this be safe and second would it really help or will it hurt mpg?

Thanks


#2

It’s unlikely to improve gas mileage. What it may do is affect the accuracy of your speedometer and your odometer in a way that would make it appear that your mileage has slightly increased. The tires would be slightly larger in rolling circumference, so they’d go a bit farther with each turn, but that will not affect the amount of energy it takes to move the same vehicle the same actual distance.

However, changing brands and/or tire type may help. When I went from an all season tire to a mud & snow tire for the winter I lost 1 to 2 mpg because the tire was a lot more aggressive and the rolling resistance was higher. I just went back to an all season tire and my mileage is back up. I track my mileage at every single fill, and I fill up a few times a week, so my data is pretty accurate.

www.carbibles.com has a great primer on tires that includes discussion of tire sizes and what they do and how they affect the vehicle’s speedo and odo accuracy. I suggest a visit.


#3

You may get the illusion of slightly better mpg because your speedometer/odometer is thrown off. The tire salesmen know this. They are just messing with you.


#4

The dealer may be pushing the 265/75R16 tires because he has them in stock.

Your old tires, 265/70R16 will do 659 revs per mile as per a tire size calculator on the internet.
The 265/75R16 tires will do 637 revs per mile which will make your speedometer and odometer run slow indicating fewer miles traveled with an apparent decrease in gas mileage as I see it, not an increase. If you correct your odometer’s error when calculating gas mileage, you might end up with a very small increase in gas mileage due to decreased engine RPMs at a given speed.

Yes, it will be safe unless you consider that your vehicle will be traveling faster than indicated which might attract attention from the wrong people unless you adjust for that.


#5

You are absolutely correct, WW.


#6

www.tirerack.com
these guys know what they’re doing and will give you a good listing of what your vehicle can and can’t take.


#7

On the Suburban, you won’t notice the increase in gas mileage. Thinner tires do help but not just one step thinner. It has to be a bit more substantial than that. The other thing working against you is that the tires will be taller than your original ones. If your tires are supposed to be 245 75R16; it might make a difference but even then, it may only seem like better mileage because you will register a greater distance every time you check it. It won’t be enough to really help.