Originally Posted by
gerry_foster
Hello all!
I've read though may posts on this topic and tried what i thought to be the correct route.
2012 f-450
stock tire size 245/75 17, new tire size 255/70 22.5
stock file has 655 rev per mile.
dash reads 60 MPH, GPS reads 68 MPH.
changed rev per mile from 655 to 578, set use VID to Disable.
uploaded tune (write calibration to ECM, write entire to TCM).
Speedo has not changed at all, still the same 8mph offset. Please let me know what i might be missing?
files attached, stock and modified.
Thanks in advance, Gerry