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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.

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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:

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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.:thumb1:

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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.

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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???

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"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..

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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?

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

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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..:doh:

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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.

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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.:thumb1:

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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.:2cents:

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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.:2cents:

Yep White01 tried to flash mine but when he pulled the tune out, so did the recalibration... So mine is off too. I average somewhere in the mid to upper 16s with the 315s, recorrected for the size. I would love to get my speedo reflashed but I worry about the cost too. Might have to check into it, it would be nice to know how fast/far I really am going. I do know that I lost about a mile on my trip to school everyday after the tires... I don't think the road got any shorter either!!:lmao2::lmao: It would be awesome to have my own Smarty but I just don't have the money for it right now and really don't have the air for the extra fuel either!!:cry: Back when I had the 285s on it, I averaged 17.8-18 driving mostly highway and better than that on long trips to Tulsa or Lawrence.:thumb1:

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Winslow the 16 your getting is that anywhere you drive? Highway city???

Yeah that's just my average, mostly highway. Right now I haven't been getting quite that b/c of the winter blend and the use of 4wd... and the skinny pedal in the snow.....:whistle::lmao2: And that's driving about 60-65, sometimes up into 70, just depends where I'm at.:thumb1:

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