Great idea
@mrrsm! Working from the Transmission Output Speed PID (221942) and factoring in Wheel Diameter & Axle Ratio data I was able to create a custom Corrected Speed PID. Compared it against GPS and got good correlation.
The PID equation details are listed below:
OBD2 PID: 221942
Long Name: Corrected Speed
Short Name: Corr_Spd
Minimum: 0.0
Maximum: 125.0
Scale Factor: x1
Unit type: MPH
Equation: ((A<8)+B)*.000371*WD/AXLE
- WD =
Effective Wheel Diameter in Inches (need good link for this data)
- AXLE = Rear Axle Ratio
OBD Header: Auto
Edit: Fine tuning of this equation likely required based on comparison of calculated corrected speed vs. actual measured via GPS. Set cruise control, note Corr_Spd & GPS speed, then multiply the .000371 constant value by a correction factor calculated as the ratio of Observed GPS Speed to Calculated Corr_Spd.
Edit #2: Fixed error in the equation (forgot to remove my wheel diameter & axle ratio)