i put on 31 inch tires and i would like to know how to figure out the millage im getting. stock was 28. The speed is off about 5mph at 60. so i figured the odometter is off. is the a way i can figure out how many miles i need to add to get the ture miles pre tank thanks

 

The main reason people want to know their gas mileage is because a big drop in gas mileage will tell you something is wrong with your truck. Just keep up with what gas mileage you are getting right now and just use that as you basis.

I got between 13 to 15 mpg on my stock tires. Upgraded to 33 all terrains and 20in rims and went down to 11 to 13. With the odometer off i guestimate im truely at about 12mpg.

If you want to completly fix it, you could buy a computer speedo correcto thingy, Programmer or something.

 

if you don't mind my asking, why exactly do you have a police interceptor badge on your truck?

 

Saw them on Ebay and thought they were pretty neat, and I thought the guys at work (I work for the PD) would get a kick out of them being on my truck. I actually ordered a couple more because my suproviser wanted a set for his F150. I seemed to set a trend, now about 6 months since mine were put on, another officer who drives a F150 lightning has the police intercepter badge on, and so does another, but its on a regular car.

Were not trying to make our personal vehicles into police vehicles or anything. We just thought it was funny.

I also have a badge on the back that says "Persuit Vehicle". (thats actually the one the officer with the lightning wanted, but couldnt find one)

 

that is a pretty neat idea

 

7mill, to find out the number of miles you drove on a tank is simple. Your speedometer is off 5 miles when going 60mph, so for every 60 miles your truck says you drove, you actually drove 5 extra miles, or 65 miles. So if your odometer says you drove 300 miles on one tank, you actually drove 325 miles, because
300 / 60 = 5
5 x 5 miles = 25
25 + 300 = 325 miles

I hope this is what your were looking to find

 

That formula will give you a pretty good estimate but will not be exact. That particular formula basically only works if you did 60mph everywhere. At lower speeds your speedo is off less, (my truck with 33's is off 1mph 0 to 20, 2mph off 20 to 40, and 4mph off from 40 to 60) therefore less miles are traveled in a certain distance, making your end calculations slightly off. However this will give you a good estimate.