I just put on my 33/12.5/15 GY Duratracs on MB72 wheels this weekend. Per everyone's posts on this forum I have noticed the speedometer is off approximately 7-8mph so I just ordered my AEV ProCal Module to fix the issues. Once it arrives, i'm not sure how great it all works but I am looking for advice on how to use this thing. I need to adjust for tire size and axle ratio. What is the formula or best way to measure the exact size of my tires to put into the module. Also, when doing the axle ratio, is this where I put that i have 3:21's? Or is there a place I have to do this as well.

If anyone has used this and can provide clear step by step directions so that i don't screw it up (i'm learning how to do most of this stuff myself) it would be greatly appreciated!

 

I used it when I put on Nitto Trail Grappler M/T 295/70R17 tires. Did your axle ratio change? If not you shouldn't have to do anything about that. The instructions that come with the ProCal are very good. But I measured my spare tire and found that they were 33.6" so I entered it into the ProCal as 33.5" (actually, as you will see in the instructions, you enter it as 33.5 - 24 = 9.5) and it seems to be off by a little. I don't know how to really check that without getting pulled over by a cop for speeding but I am checking it against those roadside speed trap things that tell you how fast you are going. They said that my speedometer is 4 MPH faster than what the speed trap thing says. So I have been playing around with it and I now have it down to 33.0" and am still 2 MPH faster. I'm not even sure those roadside speed trap things are accurate.

This probably doesn't help you much but I just figured I'd share my experience with it.

 

I did the same thing this weekend with the exact same tires and found my speedometer is not off at all maybe 1-2 miles when checking against my GPS.

I wonder if this has something to do with me not going over 60mph, maybe the faster you go the more it becomes off? That makes sense in my head.

 

The directions r well layed out. It was my first time using it and it was a breeze. I did the tire calibration and changed the tpms to zero.

 

Measure your tire with Jeep wieght on it, not the spare .. my 295 70 17 measure 32.25 at 27psi.....

 

Great point. I watched a quick YouTube video that made things seem a bit more clear on the install process. So i'm assuming i just measure from the top to the bottom of the tread and cross my fingers the speedometer is closer than 7-8mph! I didn't think my ratio would change since i'm not paying to get in re-geared.

Do you each have manual or auto transmission? I have the 2012 Auto and I am hoping my shift points from 1st to second gets a bit better.

 

Did you measure the tire when it was off the ground - mounted on the tire carrier? What size did you input into the ProCal. I have mine down to 9.00 now and still show 2mph faster.

It doesn't have to do with how fast you are going because I went past one of those speed trap things in a construction area at 55mph. Come to think of it, I checked it with my phone GPS and that reads the same as the speed trap thing. So they must be accurate.

 

Do you run your tires at 27psi typically when you are doing your DD? I have mine around 35psi i think right now, i took them down a bit from delivery. Not sure the best psi to run as a DD with interstate driving for best performance. Any advice?

 

Mine is a 2012 Auto - I didn't really notice a change in the shift points. I was coming from a 2008 JKU, so the shift points on the 2012 were awesome compared to the 2008.

 

Well, that was much easier than I thought. All fixed up and ready to go! Sucks to have paid $150 for the ProCal for such a quick fix