Spedo calibration for tire size change?
Senior Member
Joined: Mar 2001
Posts: 4,506
Likes: 6
From: Puyallup, WA
Depends....... Are you still using the same 'profile' number for the new size as well. Stock size is either 235/70/16 or 255/70/16. Are you just moving up to 265/70/16?
The profile is the '70' part of the size. It means the sidewall is 70% of the width (in this case, 255 millimeters). If so, then I'd say you would be ok.
If you go to a 265/75/16, then you will notice a difference in the speedo. Truck may shift different too, because it shifts based on speed, not totally rpms.
I went from a 235/70 to a 255/70 and did not notice any change in the speedo. Later, decided to go to 265/75/16 from 255/70/16 and noticed a big difference in speedo and the way the truck shifted. I needed to change my VSS gear to one with one less tooth.
Like kev said, we need to know the year because they only used the VSS gear in 97-98. 99 on, the speedo is done by the computer and that would need to be recalibrated to adjust for the taller tires.
The profile is the '70' part of the size. It means the sidewall is 70% of the width (in this case, 255 millimeters). If so, then I'd say you would be ok.
If you go to a 265/75/16, then you will notice a difference in the speedo. Truck may shift different too, because it shifts based on speed, not totally rpms.
I went from a 235/70 to a 255/70 and did not notice any change in the speedo. Later, decided to go to 265/75/16 from 255/70/16 and noticed a big difference in speedo and the way the truck shifted. I needed to change my VSS gear to one with one less tooth.
Like kev said, we need to know the year because they only used the VSS gear in 97-98. 99 on, the speedo is done by the computer and that would need to be recalibrated to adjust for the taller tires.
Senior Member
Joined: Feb 2001
Posts: 385
Likes: 0
Some 99s had the gear too depending on the build date. Unfortunetaly, mine wasn't one of them 
Probably the easiest thing to do is get a superchip which also has the capability of adjusting the speedo for different size tires and/or gear ratio changes. That is if you have a 99+ truck.
kev
Probably the easiest thing to do is get a superchip which also has the capability of adjusting the speedo for different size tires and/or gear ratio changes. That is if you have a 99+ truck.
kev
Senior Member
Joined: Nov 2002
Posts: 590
Likes: 0
From: Boone, IA
I got the Superchips Micro Tuner, I am going to go in and change the settings on sunday after I put on my larger tires. It is real easy and for $325 does a hell of a lot of things for your truck.