Gas mileage

Unless you're running 40"+ tires you won't be off by more than about 1 mpg. Usually less than 1 mpg.

But if you want to do it right use this site. Plug in factory size tires and the new size tires. On tire circumference you'll get a + ???% larger tire. Just as an example lets say you new tires are 4% larger in circumference. That means your speedometer and odometer is off by 4%. When hand calculating miles you take the miles driven and multiply by 1.04. Lets say your trip meter says you drove 256 miles. 256 X 1.04 = 266 actual miles driven. If you used 15 gallons of gas and divided 256 miles/15 gal.=17.06 mpg. But if you use 266 miles/15 gal=17.7 mpg.

Your speedometer will also be off by 4%. The link above will actually give you correct speeds compared to your speedometer. A 4% larger tire will only be off by about 3 mph at 70.

You also need to consider that as tires wear down they get smaller in circumference. A new tire that is 4% larger than a stock tire will be roughly the same size as a new stock tire when it is worn down to the legal minimum. Your odometer and speedometer readings are constantly changing as your tires wear.

My son works in electrical construction and usually drives 30-60 miles one way each day to a construction site. He'll work one site for months until the job is finished then move to another. He came to me a couple of years ago commenting that for months he'd been driving EXACTLY 100 miles round trip every day. For the last week he'd been getting EXACTLY 95 miles each day. Why, he asked? I pointed out that he had just put new tires on his car and they were 5% larger even though they were the same size as the old worn out tires.

 

thank you!
8.2%

so using your example of 256 would actually be 276 (really 277 since it’s .992) and 15 gal = 18.4

now i’m curious to check it on next fill up.

 

Take percentage of tire circumference difference and take difference and multiply by odometer. Let's say it's 4%. Multiply miles driven by 1.04 and you will then have an accurate mileage.

 

Lol. Yes she be dusty.

 

If my Distance to Empty stays at 410-415 or more then it's a good indication I'm driving pretty fuel efficiently. I average in the low 23s for tank mpg but I always rely on the math rather than the gauge. I think, though, the trip mpg screen might be fairly accurate.

 

199 through the redwoods in Nor-cal

 

My trucks mileage has been increasing and with just 5k miles the last fillup was 23.9m.p.g.

 

I bought one of those speedo conversion plug-ins and installed behind cluster. This adjusted the read outs. Not sure if they make one for newer trucks.

 

11 miles on the trip computer LOL