So I just put on new tires MTZs and used the procal to program the new size. In the box there are instructions that you plug in your measurement and subtract a static number (I think it is the smallest size you can set with the device) and that gives you a value that you load base on the switch position guide.
I'm guessing you did this??? If so, then what else are you thinking the AEV will do? I actually used a 100' tape (cloth fiber tape for landscape type) and rolled the tire over it and got a direct measurement. You can do the same with a piece of string and just mearure it once you know how long it needs to be to go around the tire... like measuring my belt that seems to be growing a little every year.
mine is spot on with the GPS. I can tell you the measurement for my "35"s was closer to 34"... lame. The jeep shifts fine and has power (2013 JKUR) although I can tell the tires are a little bigger.

Good luck.

 

When you set the tire size with the procal, it not only adjust your speedo and odo, it also adjust your shift point if you have an auto. I feel like with it set at 33.5 (where the speedo is most accurate) it seems to hold gears a bit too long when decelerating. So when i get down to the desired speed, it is commonly in too high of a gear. So i end up around 1000 rpms and it feels a little bogged down. This seems to be less of an issue if I set the procal at 34. I kind of wanted to avoid that though because with it set slightly larger then actual measured tire size, you are actually going a bit slower then your speedo says, which also means you are putting more miles on the odo then you are actually traveling.

 

I was having the same issue, i measured the new tires plugged in all the numbers....I didn't realize the speedo was off until I took a LONG road trip and noticed that it was off by 3-4 mph at (45mph), and at higher speeds (+75mph ) it was off by 5-6mph, based on what the GPS was saying although its not the most accurate device, i have played with the measurements a bit and got it a bit more accurate, I've got a manual so the shift points weren't an issue.

 

Hey guys,

So the procal is still working great. Mine seems to be pretty accurate still and my shift points are fine. I was frustrated that even though I had set the TPMS value so it wouldn't bother me (sold the TPMS with stock tire/wheels when I upgraded) I still had to push the button on the steering wheel to delete the "check sensor" warning. Not sure if that is the exact words of the warning but you'd know it if you saw it.

Then an interesting accident happened. I had to unhook the negative battery cable for some welding we were doing on my custom rear bumper mod. Since I re-hooked it up, no more warnings! So cool to just have the temp show up.

So, if you have the same issue, set the values you want with the procal, drive it a couple days (not sure how long it needs might be 1 minute, might be 1 week), and then unhook neg batt cable for at least 5 minutes.

Good luck.

 

My tires loaded on the Jeep measure 34.5" I plugged that number into my Pro-Cal and my speedo matches my iPhone GPS speed app and my TomTom GPS as well. I have a manual so shift points are done by me I like that control vs an auto. I would do the chalk test or take a piece of string wrap it around the spare tire and measure it. But the string method will not give you a loaded diameter.