True Mileage

[Heavyd1980]

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.

[volkswagon]

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:

[Heavyd1980]

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.

[Rogan]

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.

[Heavyd1980]

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???

[Rogan]

"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..

[Heavyd1980]

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?

[Rogan]

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

[Mopar1973Man]

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

[Heavyd1980]

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

[Rogan]

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..

[Heavyd1980]

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.

[dripley]

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.

[Heavyd1980]

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

[Rogan]

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

[Heavyd1980]

what is your ring & pinion?

[Rogan]

3.55s

[dripley]

mine too. 3.55

[Heavyd1980]

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

[dracozny]

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.