I'm just wondering how much better my truck will shift and what other differences I will see if I get the truck re calibrated for the bigger tires.

 

Not to be a smart ****....

But the correct speed?


lol

 

Yeah! let's don't overlook the obvious,huh?

 

Seriously...

It really only corrects the speed and lock up.

But...it is cheap so do it.

 

Helps not payin that huge fine b4 i go smarty

 

So it doesn't effect the shift points, but it does effect when the tc locks?

 

Fixing the speedo is nice and it also affects the shift points. That is, over the ground, actual shift points. If you now shift into OD at 50 mph and you get 10% taller tires you will actually be shifting at 50 plus 10%, or 55 mph.

So, without adjusting the pinion factor (speedo calibration) you will show the same shift points on the speedo, but they will occur at a diferent ground speed.

When I put my 315s on, the truck did not drive as well as it did later when I adjusted the pinion factor. I think part of it is the engine is working harder at a given RPM with taller tires. The computer does not know about the tires and still shifts softly. Also the acceleration is down a bit with taller tires so it's nice to get a lower downshift speed that comes with the re-calibration.

The TC lock and the shift points are based on throttle position and pinion factor, which is speed calibration based on the rotational speed of the rear axle.

 

Thank you! I want to get this done, and just didn't know how big a difference it would make.
Raspy, did you see an mpg increase?

 

I lost about 1.5 MPG with the 315s. Went to 285/70 BFGs and got back about .75 MPG. Then I went to 285/75 Toyos and got the best mileage ever. This is hand calced with a corrected speedo.

If you don't change the pinion factor with oversize tires, the computer will show lower mileage because you are actually traveling farther for each indicated mile, so more work is being done. But don't trust the computer for mileage numbers. Hand calc to see how far yours is off then you can use the computer and correct the reading for a rough mileage number or to show trends.