I just bought a Predator to correct my speedometer and stack with my Edge J/A. I set the gear ratio at 4.56,which I have and the actual measured tire height for a 315/75/16. My 37s measured 17.5" from the center of the wheel to the ground loaded,multiply by 2 and you get a 35"(315 equivelent). The problem is the speedometer still reads just under 20% fast,checked for 5 miles on the interstate mile markers. Am I doing something wrong? I know decreasing tire size input will fix it,I'm just disappointed the programer is not more accurate.

If you find out how to do this let me know. I have 285's on stock rims. If anyone can tell us please help

Did you check the accuracy of your speedo before you made the gear & tire changes? My point is maybe it's not the programmer, but the way the PCM is calculating signal input. My brother made a gear change in his '99 1500 and had the PCM reprogrammed, but no matter what he does the ABS light is on and the scanner says that the front and rear ABS sensors are reading different speed inputs. Just a thought.
JP

You have to go through Modify tune, then back out and install modified tune I believe. I've had occasions where the Tune was installed without the modification. I'd suggest using a GPS if available.

Regardless of accuracy based on input specs, the Predator allows you to tweak it by inputting tire sizes that do not exist. I'll also add that speedo accuracy appears to be non linear on the OE gauge. In other words it may be on at 50, off at 60, and on again at 70mph...

Not sure if what happened to me is the same thing here--but when I FIRST used the predator to just correct the tires--I actually measured worst calibration. In other words--stock is 245 tires--I have 265--about 4% low on speedo. After Predator adjustment--I was now about 8% low!

I reloaded stock program and then reloaded everything all over again. The speedo now reads correct.

The ABS light will be on for any large gear changes or large tire changes as it is not calibrated. The ABS is seperate from the speedo calibration and need to be corrected along with the speedo when large size changes have occured. If the calibration is truely working as it should with the programmer the speedo should be correct, but you may get the ABS light until it too has been fixed.

My ABS light and brake warning lights have both come on 3-4 times since I did the recalibration with the Predator. How do I modify the ABS sensor to read correctly and kill the lights.