Seeing it more and more. Had to make this post and lets spread this info around. Everyone says oh my mileage is so low with xx tire size. Chances are its not bad at all. If you dont know the exact miles driven everywhere you go with larger then stock tires or have a matched speedo gear for your tires your not even close to right with mpg calculations. 32" tires or less should only effect mileage by 1-3 mpgs. They are heavier.

31" your odometer is off 18% thats 51 miles off every 300 you drive
32" is off 22% thats 66 every 300.

Bigger the tire the more its off. However 33" and up the tires do get heavier and will have more actual effect on mpgs.

So lets stop telling people theyll get 10 mpg with 31" tires, etc. I get 17.5 mpg with mine and thats about 75% highway. Just got to know how to figure it out.

 

You are sort of right... if you have larger tires then the faster you drive the further off your speedometer is going to read compared to your actual speed.

 

IMO Keeping it tuned up, Clean Filter and Plugs helps alot too..

 

Thats why i listed percentages. The faster you go channges the amount your off but not the percent.

 

I Guess I should read a little better huh lol

 

so you are saying with 31's at 18% will come out to about 250 miles a tank but you are actually getting around 300 miles?

 

How would I sync it up correctly so it's reading it right? or am I just always going to have to add 60 miles to a full tank?

 

okay do the math on this one.

I'm running 33's, stock 3.55's
my last tank from topped off to low fuel light I got 165.4 miles. I topped it off, it took 15.47 gallons. based off indicated mileage only it averaged 10.69 MPG. what is reality?

 

I use a gps for my speed and trip meter and by going off that I get 20 mpg on the hwy

 

where did u get 18% from? I keep trying to find some info on this posted somewhere else other than on a forum. With my calculations ( i only went by the percentage of how much bigger the tire were from stock) I got 11.3% with 31's

 

So I am running 31's and using GPS police radar and running a course that the exact milage is know I came out with 10% difference on my Odometer so 10-11.3% is probably pretty acurate for 31s

 

Use this calculator to find the difference in tire size. http://www.google.com/url?sa=t&rct=j...08iM8nnZeMaGvA You want to look at the speedometer difference, NOT the diameter difference in red. The circumference of 31's are 9.5% larger, 33's are 15% larger, 35's are 23.9% larger.

Yay math! So with 33's you got 165.4 indicated miles, multiply that by 115% to get your actual miles. 165.4x1.15=190.2. So 190.2 miles/15.47 gal = 12.29 MPG. Still pretty bad but not as bad as you thought.

 

Not sure where either of you are getting your calculations. Stock size is 225/75/15. Which means the sidewall is 225mm x 75% = 168.75mm or 6.64".
So the tire diameter is 15" + (6.64"x2) = 28.28".

So 31's are 2.72" larger. 2.72" divided by 28.28" = 9.6% larger than stock. Or you can just use the calculator I posted above

 

sweet, thanks!

 

i used a calculator i found that gave me those numbers from a yahoo search. im not sure how it does it but i know my work route is 66 miles a day and it calculated really close to the mileage i was reading on the dash. it could be wrong but nothing online is ever wrong