2016 sierra

[GMCZilla]

I have a 2016 sierra with BTR stage 2 cam, dod delete, vvt lockout, custom tune?

I noticed my speedometer calibration was showing 30.8? tires entered, and my factory tires are 275/55/20 which is 31.9?

I used the calculator conversion and tire wizard and now Speedo is off by 3+ mph faster than actual. When I return to original values, Speedo is with .5-1mph per gps. There are a few other values in the gen v that I?m not sure are correct.

The vss tire revs dist and dist-trans had separate values originally. 640.52 and 652.32
Driven and not drive tire circ were at 98.8 and calculator bumped them to 100.236.

Just feeling if everything was verified via RPO codes for gear ratios and actual tire stickers vs tires that I shouldn?t see that big of a difference between actual and previous settings.

[GHuggins]

HPT's tire calculator has never worked right. You always have to enter in a slightly smaller size. You have to watch out with certain 4 speeds using it too. I've had it go into neutral on them because of the calc screw ups.

[2xLS1]

When using the wizard always subtract .8" from what a tire size calculator shows for tire height. Been that way on GM calibrations forever.