Mileage and Larger Tires

Ok so I just upgraded from my stock 265/65R17 tires to some new nitto tera grapplers 285/70R17 and I always hear the complaint that larger tires will decrease your gas mileage and I was curious as to how much this truly affects it.

So I am assuming that with every rotation of the wheel the odometer counts this distance traveled and the circumference of the stock 265/65R17 tires on the 2nd gen is 8ft. So therefor the wheel must rotate 660 revolutions to travel one mile.

The 285/70R17's have a circumference of 8.56ft and must rotate only 617 revolutions to go one mile.

Basically I calculated that for every mile traveled on the odometer you would in fact travel 1.07miles with the larger tires.

Has anyone else done this or am I the only dweeb????.

So it seems to me the gas mileage decrease should not be as bad as it sounds and I will be testing this.

If you fill up your tank with larger tires multiply your mileage at fill up by 1.07 and that was your true mileage traveled. Then divide that by how many gallons you put in.

Also larger tires it seems would benefit the miles recorded since you are traveling farther with every rotation.

every 100,000 miles on the new 285/70 tires would actually be 107,000 miles.

 

bump

 

So.... for warranty you would get an extra few thousand out of it?

 

If a train leaves New York traveling 63 MPH.....

 

That is true if you have a tire that, while taller, weighs the same and is no wider than the first. Weight and width negatively affect mpg. Wider tire = more friction. Heavier tire = more juice to make it move. Normally the extra distance gained per revolution doesn't come close to the extra effort to start and keep moving.

 

No, you're not the only one. I use a similar equation to figure out my gas mileage, accurately that is, with the larger tires.

I had also thought of using an on board GPS system to figure the mileage, but after some thought i concluded that this would not be as accurate as figuring the conversion without rounding too much, or at all for that matter. The problem with figuring mileage through GPS systems is that any system you could purchase for your vehicle runs in an Autonomous state. Your positioning is rarely, if ever fixed and definitely not going down the highway. Not only that, it can not accurately depict turns, due to taking multiple snapshots per minute. The only reason why i know this is because i specialize in GPS Surveying and automated machine control processes. Sorry for the rant, but I hear people doing this way too often.

 

Dont know about the train one sorry lol

just wanted to provide some insight because i remember longhorn saying he was down o 12mpg which i thought was nuts but who knows.

i will have a decent estimate sometime in the next 10 days of where my mpg is using my lil equation =)

 

In the end your gona lose 1-2 mpg

 

FYI, there are tons of tire size calculators available on the web. They'll do the heavy math for you. You're calculations to figure out fuel economy are correct. On my 02, the 33/10.5/15 BFGs hardly affected the fuel mileage.

 

Actually a taller tire will be harder to turn even if the weight is the same as the shorter tire. Inertia increases as a square of the distance. An example is a figure skater. When the figure skater's arms are tucked in, she spins easily but when her arms are out it's harder to spin that fast. Whether her arms are in or out, she weighs the same. If you add weight, that will only compound the problem.

 

I use a similar factor when calculating my mpg. Since I have a 2wd base, the tire sizes aren't the same, but the formula basically is. I multiply by 1.117.

Old size=215/70/15
New size=30x9.5/15

I don't know how bad the mpg suffered on mine. The tires were already on it when I bought it.

 

What if you used a Scangauge to give you fuel GPH and going down the interstate at 55 mph (based on a GPS and not your speedo). Then do your math based on results at a 55 only.

 

Good point. I wasn't thinking that a significant percentage of the weight of the tire is around the circumference.

 

So what did you figure out?

 

18mpg before lift and tires, 17mpg after lift and tires, maybe even less now that I put on my exhaust. :-(

 

I can live with 17, I may have to start shopping around for a lift
Thanks!

 

I figured this out an easier way.... the mile markers on the interstate.....lol.... that gave me a round about conclusion