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.

well thank you sir I appreciate that. Hopefully I can get my smarty fixed soon and then have the ability to do this my self.

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.

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!! 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!! 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.

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

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..... And that's driving about 60-65, sometimes up into 70, just depends where I'm at.

well thats good to hear. thats about what mine does on the highway when we go back to fayetteville. thanks man.

well thats good to hear. thats about what mine does on the highway when we go back to fayetteville. thanks man.

Welcome, once I'm able to afford a Smarty or have a dealer flash it, I'll know more accurately.

kinda off the subject but how do you like the short shifter????

kinda off the subject but how do you like the short shifter????

I really like it, helped tighten it up and make shifting more fun!! Kinda like a big sports car!

thats sweet man!!!

thats sweet man!!!

Oh yeah it was worth it and wasn't hard to install either!!

Since the smarty isn't for everyone I'd certainly give this a look see. I havent installed or used one myself fwiw http://www.superlift.com/accessories/truspeed.asp Now to contribute, I average just under 20mpg driving 40% city 60% highway.6 speed 4x4 315/75/16's. I do relatively short warm ups, good air pressure and always leave my house in plenty of time to reach my destination, driving habits dictate whether I get 14 mpg or 20.

Since the smarty isn't for everyone I'd certainly give this a look see. I havent installed or used one myself fwiw http://www.superlift.com/accessories/truspeed.asp Now to contribute, I average just under 20mpg driving 40% city 60% highway.6 speed 4x4 315/75/16's. I do relatively short warm ups, good air pressure and always leave my house in plenty of time to reach my destination, driving habits dictate whether I get 14 mpg or 20.

Cool deal man, I'll check into that!!

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.

Going here might help http://www.grimmjeeper.com/gears.html as far as helping to figure how far off you are,you can compare your stock drivetrain/tires vs. new tire size.

Going here might help http://www.grimmjeeper.com/gears.html as far as helping to figure how far off you are,you can compare your stock drivetrain/tires vs. new tire size.

Thank you sir! and congrats on the 800k!!!

guys, the thing to remember is it is a percentage. the faster you go, the more they are off (bigger or smaller) 5% of 100 = 20 but 5% of 200= 40. it is still 5 %, the same with tires, you can only estimate MPG, but speed is easy, look for a radar detector that post your speed. my 31s, i was driving 2mph fast at 25 and 5mph to fast at 60. drive slower for oversize tires to avoid tickets

this is absolutely correct..

guys, the thing to remember is it is a percentage. the faster you go, the more they are off (bigger or smaller) 5% of 100 = 20 but 5% of 200= 40. it is still 5 %, the same with tires, you can only estimate MPG, but speed is easy, look for a radar detector that post your speed. my 31s, i was driving 2mph fast at 25 and 5mph to fast at 60. drive slower for oversize tires to avoid tickets

Yeah mine when it goes through the speed checker shows that I'm going 64 when my speedo says 60.

that truspeed box is really meant for a vehicle that has tires beyond the size limit in the ABS which is somewhere in the 40" range if i remember correctly. below that I would just look into getting a http://www.hypertech.com/products-speedometer-calibrator.aspx plugs in just like a smarty but only deals with the tires, and on a plus it pulls your DTC's too. i don't own this but I have a hypertech III that does the same thing plus some tuning.

that truspeed box is really meant for a vehicle that has tires beyond the size limit in the ABS which is somewhere in the 40" range if i remember correctly. below that I would just look into getting a http://www.hypertech.com/products-speedometer-calibrator.aspx plugs in just like a smarty but only deals with the tires, and on a plus it pulls your DTC's too. i don't own this but I have a hypertech III that does the same thing plus some tuning.

I might look into that, it would be nice to have the right speed!!