Speedometer - Transmission Calibration

[Ch2500HD]

I have a 2003 2500HD with the 6.0L engine. I want to replace my 245/75/16 tires with 285/75/16's. I bought a Hypertech PPIII to calibrate my speedometer, but after reading all the warnings in the booklet I dont feel comfortable messing with the computer. Any ideas about how the truck would be affected by installing the new tires without changing the speedometer calibration. i.e. any drivetrain damage etc. or will my speed and odometer just be off.

[Shaners]

I would think if you don't change your settings that your speedo would just be off ... that's all... no drivabillty issues.

 

 

However, I don't see why you wouldn't reprogram for the larger tires.

 

I think the reprogram for the larger tires is more of an issue with the Allison tranny and not the 4L80E.

[mmmikkke]

I have a 2005 2500HD with 285's, and the computer is still set the way it was when I bought the truck. My speedometer is off by 5mph at 65; when it reads 65, the truck is actually going 70. I've gotten used to it and it doesn't bother me at all. I like keeping the torque converter lockup speed where it is; if I reprogrammed for the larger tires the torque converter lockup would occur 3 or 4 mph sooner. I would dislike that more than I dislike the speedometer being off by 5mph at 65.