troy_v

I wasn't sure which subforum would be best for this question, so it went here.

I replaced the stock Pirelli's with 33" (275/60R20) Cooper Discoverer A/T3 tires. There are 1" taller than stock, which results in the truck going 3.4% faster than what the computer assumes it's going on the stock tire size. I can easily do the math in my head when driving to convert the speedometer reading to actual. And I hand-calculate my fuel mileage taking this 3.4% difference into consideration. Given those things, are there any other reasons I should try to reprogram the truck's computer to reflect this new tire size?

I've heard that some programmer's have the feature to reprogram for certain tire sizes. I've also read that there are several tire sizes stored in the computer's memory which the truck can be set to, provided you need to change to one of the few in its memory via a Ford Dealer. Is there anything else I need to know about these two programming methods?

tastysalami

Your odometer is going to give you the benefit for the 3.4% difference. I wouldn't change it.

Fishhawk460

I also replaced the stock Goodyears with 33's. At first my speedo was off by a couple MPH at 70. This was in the summer of 2010. After a few months I noticed my speedometer matched my speed. I've been told the computer can't reprogram, but I'm spot on now.
I talked to Ford right after I bought the tires and was told that Ford cannot reprogram a larger then stock tire on the F150 because they can only program the truck for what the factory offered. Their software is not writen for anything other then stock. If you really want to reprogam the computer for a one inch increase in tire size you will need to buy an aftermarket programer.

CLABRO

No need to mess with it. 33" tires aren't going to change it that much to even matter.

JLonsinger2011

If knowing how fast you're going doesn't matter to you...