So I went from stock tires to 33's and changed my diff's from 3.71 to 4.88. Then I bought an AEV ProCal Module to tell my JK's computer about the different tire size and gears, and then checked it on a 50 mile stretch of I5. All was well.

I just had a problem with my ABS, so, as AEV tells you, I unloaded the custom settings and restored the stock computer settings before taking it back to the dealer. (issue was a broken ABS sensor). However while riding around since without re-adjusting the JK's computer, I have noticed that my speed is spot on, just like after I made the adjustments. It seems going to bigger tires and 4.88's cancelled each other.

So now the question ... does the JK's computer that does ABS, anti-roll, anti-spin, etc really care about diff ratios and tire sizes, or does it just care that it is correctly reading the true wheel speed at each corner? I'd prefer to not use the ProCal and not have to re-customize the computer settings and then reset every time I take it in for service. My gut says it just cares about wheel rpms correctly translated to true speed, and doesn't really care if its a 3.71 or 4.88. Anyone know more about all these electronics?

thanks
Kurt

 

The Pro Cal was probably a waste of money for you if you JUST got it to reprogram the speedo. You're right. Going from 3.73 to 4.88 and adding the larger tires put you right back to stock as far as RPM goes. I think the Pro Cal does other cool stuff though.

 

Tires and gears don't cancel each other regarding speedometer reading.
The computer gets speed reading from the left front wheel according to the FSM, and verified by the AeroForce gauge. Only tire size will influence the speedometer.

I checked out your "My Conservative Sahara" page. Nicely done!

 

Can they correct this at the dealership?