AEV Procal Troubles

Rippin Lipz

Rippin Lipz

New member
I have a 2012 JKU Rubicon with an automatic transmission. Just installed a RK 3.5 lift with 38" tires. I'm currently still using 4.10 gears. I used the AEV Procal to correct the tire size. Well something just doesn't seem right. The transmission will shift all the way to fourth, then it just stays there. I have to use the tap shifter to get to fifth. I was kinda playing around with it today and I was at 4500 rpm's in fourth gear. I just held it at 4500 rpm's just to see if it would shift to fifth. Well, it never did.

So, is something wrong?
Or is it because I'm using 4.10 gears with 38" tires?
Or maybe something else?
 
wayoflife

wayoflife

Administrator
Staff member
Did you make sure to physically measure your tire from the ground to the edge of its shoulder (the corner where the side wall turn 90 deg into the tread)? It is important to do this and if you didn't, you most likely have a size input that's too tall and that'll throw off your shift points. Being that you have a 38" tire, I would bet your actual tire size is closer to 36" or there about.
 
Rippin Lipz

Rippin Lipz

New member
What I did was put a level across the top of the tire and measured from the ground to the bottom of the level. With 30 psi I got 37.75. I also measured them with 27 psi and got 37.25. I have MTR/k's and heard that they're pretty true to size. Should I be doing it a different way? Thanks for the help.
 
wayoflife

wayoflife

Administrator
Staff member
Rippin Lipz said:
What I did was put a level across the top of the tire and measured from the ground to the bottom of the level. With 30 psi I got 37.75. I also measured them with 27 psi and got 37.25. I have MTR/k's and heard that they're pretty true to size. Should I be doing it a different way? Thanks for the help.
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That would give you an incorrect reading for the purposes of calibrating your speedometer. As mentioned, you need to measure up to the corner of your your tire's shoulder - NOT the top of the tread like you did.
 
wayoflife

wayoflife

Administrator
Staff member
Rippin Lipz said:
Ok great! I will remeasure first thing tomorrow. Thank you for your help. :thumb:
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No problem. If you have a GPS unit, go ahead and verify your speed after doing it the way I just described. I can guarantee you that it'll be right where as what you have now is wrong. That should help to fix your shift points but, let us know if it doesn't.
 
Rippin Lipz

Rippin Lipz

New member
Well that made a HUGE difference! The tires measured between 36.75" and 37". I programmed for 37" and it rides like it did stock. I'm so pumped! My speedo is dead on up to 50 mph, then it's slightly off. I'm gonna try 36.75" and see what that does.

Thanks for your help!
 
wayoflife

wayoflife

Administrator
Staff member
Rippin Lipz said:
Well that made a HUGE difference! The tires measured between 36.75" and 37". I programmed for 37" and it rides like it did stock. I'm so pumped! My speedo is dead on up to 50 mph, then it's slightly off. I'm gonna try 36.75" and see what that does.

Thanks for your help!
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Glad to hear that helped. I would defintely go 36.75" - that's about what I was thinking you should be at anyway. When you have it on, it'll be on all the way across the speedo spectrum. :yup:
 
Colorado4Wheeling

Colorado4Wheeling

New member
Would another method be to measure from the ground to the middle of the hub - then multiply times 2? this should also give you the number you are looking for - or at least one to try.
 
wayoflife

wayoflife

Administrator
Staff member
Colorado4Wheeling said:
Would another method be to measure from the ground to the middle of the hub - then multiply times 2? this should also give you the number you are looking for - or at least one to try.
Click to expand...

Yup, that works too. The method of measuring to the corner of the shoulder just doesn't require any math :crazyeyes:
 
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