I have larger then stock tires on my F150. This affects my speedometer, along with my odometer (right).

So what would be the best way to calculate my gas mileage, since the miles traveled divided by gallons used will not work.

 

are those numbered signs...those are milage markers...take truck through one set of those and record actual reading on speedo then do calculations from there(actually odometer)

 

Good idea, thanks. Someone else gave me this web-site, according to it (assuming I am reading right), my odometer is 5.54% off.

So I will do it both ways and see if the highway marker thing verifies what this web site is telling me.

http://www.c5-corvette.com/tirecalc.htm

 

Get someone with a vehicle with an accurate speedometer. Drive behind them at set speeds and note what your speedometer reads.

If you have a mechanical speedometer, there are gear over/underdrive units that mount between the transmission and speedometer cable. By using the right gear combination, you can get your speedometer to read correctly. I've gotten one once at a speedometer shop.

Good luck

 

go to the dealer, and get the VSS gear for a pickup w/ the 265/70/17 tires, which are the same outside diameter. i did, and it only cost me like 12-13 dollars. i believe it was a 19 tooth. ask Mitch150, he told me all about it.