My questions is. Does anyone know weather or not a dealer can reprogram your computer in your truck when you get bigger tires, or would I be better off just getting a programmer, super chip, edge, etc?

 

Isnt it just a good excuse for getting a tuner? I would assume the dealer is able to do something like that but i could be wrong. I have a xcal2 so i didnt have to worry when i put on my new tires.

 

Yes they can, although the selection of sizes available in the program are limited. I just put on a set of 275/70R17s on my truck replacing the 235/75R17 that came with the truck. I had them program it with the 275/65R18 size as that is the same final diameter as my tires. That is about as large a size as their programming is. Other sizes I saw listed on the screen were the 255/70R17, 265/70R17 and some smaller ones.
If you need more sizes but don't want to go the full programmer/tuner route, Superchips has a programmer called Tirepaq that just does the tire size and shift points. It will also read codes.

 

You can also modify the rear gear ratio. Last time i did it i was able to get within 2mph @ 60 for 35s on the stock programming.

 

Its a good idea to get your computer reprogrammed with the proper tire size. Different sized tires not only affect the speedo, they affect the odometer, tranny shifting, and abs braking

 

Yes you can tell the computer that you have a 3.55, 3.73, or 4.10, but what that will do to the shift points, I am not sure.

 

Nothing, F-150 shift points are MPH based. But have MAX RPM shift point also.

 

Which means it will be affected as changing the gear ratio will change your speedometer reading.

 

Yes, i just phrased my response akward.

If you really want to get into it the PCM actually uses a value of N/V to determine vehicle speed, odometer output, shift points, etc.... N/V is the 1:1 ratio between the engine and the drivetrain and calculates 1st, 2nd, 4th from the gear ratios in the PCM. N/V is a parameter in the PCM that is set, but also "leaned" and calculated from the tire size and axle ratio.