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I just picked up some Nitto Trail Grapplers, size 285/65/18. Had them shipped and they arrived with 36psi in them. What is the idea air pressure for these? The Jeep is a daily driver. I also have a ProCal to set the TPMS settings, I just don't know the best pressure to run in them...
 

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I have P285/70-17 Nitto Terra Grappler's - I am running 32.5 psi all the way around (cold) and the chalk test (performed after the tires were warmed up) showed good contact all the way across.

I used the Pro Cal to adjust my speedometer but did not mess with the TPMS settings and I have no TPMS lights.
 

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i have terra grapplers on 35 12.5 18. I was ridden rough so lowered pressure to 26psi in front and 24psi in rear. made big difference.. is this low?? where can i get the programmer that'll get my light off.
 

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i have terra grapplers on 35 12.5 18. I was ridden rough so lowered pressure to 26psi in front and 24psi in rear. made big difference.. is this low?? where can i get the programmer that'll get my light off.
You really need to do a chalk test to see how the tread is in contact with the ground to determine correct air pressure.

As for the programmer: AEV ProCal
 

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1 - Drive to a flat area. This can be your driveway or the street in front of your house. Just make sure there aren't a lot of cracks, bumps or pot holes in the ground.

2 - Draw a thick, straight line across the width of the tire.

3 - Drive the car forward at least one-full car length.

4 - Inspect the chalk on the ground and on the tire. A tire with the proper air pressure should press the chalk line evenly across the ground. This means you'll see the entire chalk line imprinted on the ground. An over-inflated tire will bulge and only the center of the line will touch the ground. You'll only see a small portion of line if this is the case. If you're tire is underinflated, you'll see only the sides of the lines since the middle of the tire is not making contact with the ground.

5 - Adjust your tire's air pressure according to the chalk test results.
 
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