Just finished programming with the Rough Country Speedo Calibrator and now my speedometer is off in the opposite direction. Running 35's it was originally 5 MPH slow, now it's 4/5 MPH fast. Anyone have/had this problem? Should I reprogram again using 35 in tires as the input or just put 33 and see what happens. Will reprogramming several times mess anything up?

 

When you broke out the tape measure, what did you come up with? My last set of 35's measured 33.5" at my typical inflation, when sitting under the weight of the jeep. That is the number I put in the programmer as a starting point.

 

You are spot on. The 35's only measured 33.5. However, it didn't seem to change the speedometer calibration. It's still 4-5 MPH fast. I guess I'll call Rough Country and see how precise the programming is. Maybe typing in 33 will have more of an effect.

 

A couple thoughts: First, that calibrator is may have a software update on their web site. Second, just split the difference between what diameters (or circumference) resulted 5 slow and 5 high.

 

Internet update only works for Windows computers???? Mac has been around for 30 + years!!!! My frustration is growing. I should have gone with a Procal.

 

I don't know what top-secret formulas the different companies use in their programmers/tuners, but apparently they are different. From my experience, I could never get the Superchips Flashpaq closer than 3-4 mph to what the gps showed. (and that was after wasting an afternoon with constant stops to make 1/4" tire size adjustments away from measured height.) The DiabloSport InTune was a bit better. And the AEV ProCal has my mph within 0-2, depending on speed. May just take some trial and error, but yeah, I wouldn't be happy if the closest I could get it was 5 mph...

 

After some trial and error I think 33' is the right input. I think I'm within 2 MPH. Hopefully this thread helps other people who decide to use this product. As always, thanks for everyones help.