Can anyone tell me if calibration is an "exact science" or "trial and error" thing with the Predator?

I've been running the 33" Toyos for a while now, so maybe I'm just used to the speedo being understated, but I received my Predator from JK the other day and immediately put in the 65HP tune, once I modified the tune to go from 245's to 285's. Speedo now seems too high. Unfortunately I don't have access to a GPS, and if I try to run at 60 MPH on a freeway here in AZ, I'll get run over. Any help would be appreciated.

Take a tape measure out and measure how far it is from the ground to the dead center of the wheel tire combo on both rear tires. Take the average of the two double it and you have the "rolling diameter" of your tires. get that entered into the predator and you should be fine.

I am assuming that you could enter a 33 12.50 16 into the predator if you wanted. If not there are 25.4 mm to an inch. just do the math out and get the metric equiv. tire size.

i would try trial and error myself. I have been trying to figure mine out lately. i believe my problem was that the dealer went ahead and upgraded my tire size to the 255/75/16's that his programmer could do. i have now tried to program mine to the 285's but it was too slow yet. i now have it on the 293/74/16 and it is pretty close. when i had it on the 285's i was off about 5 mph @ 60.

Going from 245's to 285's would be a significant difference. To get an exact measurement make sure you have the correct air pressure and put a dab of paint on the tire center tread roll the truck and measure the distance between the marks left on the cement. The measurement will be exact.

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