I recently replaced the OEM tires (Michelin 245/60/17) with Bridgestone AT Revos 265/70/17. Nice tires. Anyway, per the truck's computer, the MPG has gone down. I figured that my speedometer would be off but didn't know about my reported mileage. Have the larger tires reduced mileage? is the computer reading wrong? or both? Guess I could check mileage the old fashioned way but I've come to like the computer. Thanks in advance. Jim '03 1500 QC 8 Ft Bed

 

The computer reading is wrong because the main computer still "thinks" you have 245/70/17 tires on your truck. You need to make an appointment at your dealer and have the main computer reset for the new tires.

 

Another option is a "Tuner". There are a few companies that make them. They plug right into the computer. From what i understand it's a simple interface with yes and no questions that takes 15 minutes or so and you unplug it and your done. It will fix spedo and mileage problems as well as add horse power by adjusting the comp.
I recently lifted my 03 1500 5.7L and am now running 35's so my computer is confused as well. I hope to purchase a tuner in the next couple of months.

 

ce2flaco, Mazz,

Thank you for taking time to reply. Not sure what I'll do right now. Santa has tapped out the budget at our house so whether I buy a tuner or take the truck back to the dealer it'll have to wait til the new year. Again thanks,

Jim

 

A trip to the dealership will be a whole lot less than a "tuner". Most dealers will do this for less than $40, although some charge more and some will do it free of charge. I guess you could call the dealer and ask what if anything they would charge. It only takes them about five to ten minutes.