Ok guys I have 315-75's on my truck and I believe that my mph is off about 13% so if i am trying to calcuate my correct mpg would i take my total mpg' per tank and multiply by 13%??? :shrug:If i am thinking right this should give me an accurate mpg. Any help is much appreciated.

Just out of curiousity why wouldn't you get the computer reflashed to accomodate the big tires? Besides then your speedo would be right too! I got mine done when I put on my 285's and they didn't even charge me to do it:thumb1:

the only reason that i havent is because of the cost! i figured it would be at least the normal one hour shop fee! but thank you i will look into that.

you're pretty close, heavy.. ~13.5% is a touch more accurate. 60mph actual should show around 68 on the speedo. But it won't be truly accurate.. and adjusting the percentage (as I've done here) doesn't produce accurate numbers.60mi + 13.5% = 68.1.so 300mi actual = 340mi odosince you'll be needing to calculate backward, you'll do:340 - 13% = 296.. (diff. of 4)It's not dead nuts on, but it'll get you close. The more mileage you calculate (i.e. 400mi) the further your math will be off... 400mi + 13% = 452.452 - 13% = 393 (diff. of 7)BTW, how do you run 315s on a leveling kit? I've got 295s + 2" leveling, and I barely clear. I mean BARELY.

the leveling kit was on it when i got it. but its a pretty good size leveling kit i think the spacer is about 3" by looking at it. and my tires rub in a full lock going in and out of my driveway and other places that the suspension is working in this configuration. so what you are saying is that i need to remove 13% from my mileage to be accurate???

"accurate" is a loose term, here .. "somewhat accurate" is better..But yeah, given that you average in the 300s per tank (?) than you could stick with the 13% to rough estimate what the calculations are.I know running my 295s, my odometer (uncorrected) would hit 300, and my GPS would show ~ 330ish..

yes my very last tank lasted 330 by the truck odometer. so by the math i should be somewhat close to 374 miles which comes out to around 15 mpg. right?

depending on the gallons you put in, yeah..my last fill-up (earlier this week) was 22gal, 284mi.. how awesome... 12.9mpg.

  Rogan said:

depending on the gallons you put in, yeah.. my last fill-up (earlier this week) was 22gal, 284mi.. how awesome... 12.9mpg.

i think with my in town drivin thats about what i average!:banghead:

I miss my 12v. Same driving style, same trip usage, averaged 17mpg.. I don't think I've ever seen 17 in this truck, even highway..

I dont know how folks like Mopar, White01 and TH are getting the mpg's that they do. I would love to get in the upper teens.

i am getting 19 to 20 mpg on the highway and 15 to 16 mpg in town depending on how heavy the right foot is. been like that since it was new. i am running 265 75r 16s. that makes a bit of differance also.

what kind of gears are u runnin? i bet that 6 speed helps alot! i would be super happy with those numbers

My numbers above are with 265-70/16s, 6speed, bhaf, and 5" tbe...

what is your ring & pinion?

3.55s

mine too. 3.55

wow 3.55's i would have figured you would do better than me since i have 4.10's!!!

  Heavyd1980 said:

the only reason that i havent is because of the cost! i figured it would be at least the normal one hour shop fee! but thank you i will look into that.

If you have a SMARTY, you can recalibrate the speedometer. However, if you use anothers to load in the calibration and then take the SMARTY off, you will loose the calibration.