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Old 08-02-2011, 01:08 PM   #1
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psi question

just put on some general at2 grabbers on my jk. they are 33x10.5

the tires say the max psi is 65
the guy that put them on filled them to 50psi and the thing rides horribly/ i feel every bump in the road

i dropped the tire pressure to 35 psi for road use... is this too low or too high? the car door says on psi, the tire says another and the installer filled it to another... i am totally lost.

35psi feels right for the car but there is a small bulge at the bottom of the tire that tells me it might be under inflated

any suggestions?

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Old 08-02-2011, 01:36 PM   #2
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When I got my 93 (32x11.5.15) it had 32psi and rode very rough as you described. I'm running 25psi right now and the ride is much smoother. Max according to the tire is 55psi - but remember this is the MAX. Just guessing I'd say the 35psi you are running is still too much.

I arrived at 25psi by doing the "chalk test". Make a straight line across the tread of the tires from one side to the other and drive around a little so that the chalk can wear off. If the chalk wears off the tire evenly you have arrived at the proper air pressure. If it wears off in the middle of the tread but not on the outside then the pressure is too high. I'm not sure this is an exact science - some people swear by it and others say it doesn't work - but it worked for me.

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Old 08-02-2011, 03:40 PM   #3
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Door sticker is for stock size tires, which being smaller, require more air. MAX on the tire is the most you should ever have in them..... Far too much for as light weight vehicle as a Wrangler is...

Buddah is right, chalk test is pretty good method. Keep the edges off the pavement for the best ride and to keep from under inflating them. The ride quality and handling will be your best guides. Depending on the load range of your tires and wheel width you will probably find somewhere between 26-33 psi is your best bet....
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Old 08-02-2011, 03:51 PM   #4
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I run my 33 x 12.5's at 27lbs. Anything more is to hard. Off road run them at 12lbs on 8 inch wheels.
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Old 08-03-2011, 07:31 PM   #5
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thanks

thanks everyone. i will run the chalk test this weekend!
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Old 08-05-2011, 04:28 AM   #6
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The chalk test is an old method used for decades, but take into consideration wheel width as this will effect the test. Trial and error will get you there. Seat of the pants feel it out. I run 34 psi in 33's. Seems best to me....
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Old 08-05-2011, 04:40 AM   #7
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I run exactly 30psi in my 33 10.50 15 KM2 on the street and 18-20 psi on the trails. On steel 15x8 rims.
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Old 08-05-2011, 12:45 PM   #8
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I run exactly 28psi in my 33 10.50 15 KM1 on the street and 8-12 psi on the trails. On alloy 15x8 wheels.
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Old 08-05-2011, 03:45 PM   #9
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I have BFG KM2; 265/75-16. The weight on my front axle is 2200 lbs and 2500 lbs on my rear axle. I run 22psi on the front and 25 psi on the rear, per the load infaltion chart for my tire, I'm 16% over inflated for the road.
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Old 08-06-2011, 11:41 PM   #10
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Good info here. I never heard about the chalk test. I have 35's the max is 65 I had it at 50 psi. After reading this thread I dropped it down to 30 psi much better ride. I couldn't do the chalk test because it rained today.

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