[THUNDERA]

Originally Posted by eddiekidd

The way I understand is like this. Your computer is set from the factory with a specific size tire. Our trucks computers are not able to learn a new tire size without being calibrated for them. If you change tire size, whether bigger or smaller, the shiftpoint will remain calibrated for the stock tire, causing the truck to shift too soon if you went with larger tires or too late if you went to smaller tires. A small change in tire size probably doesn't effect it a lot. Again, that's the way I understand it.

This is what I was thinking - but its backward. With larger diameter tires the ECU thinks the vehicle is moving slower than it actually is (if its reading the speed sensor). So if the wheels are actually rotating slower for a given speed wouldn't the ECU delay the shifts to compensate?

I have the 33" BFG's They are appox. 1.5" bigger than stock so I calculated that I am actually travelling 4% faster and farther than indicated.

Can the dealership re-calibrate for the tires? Or do I have to buy a tuner?