i finally got some chauk from wally-world and gave my tires a little rub down.

i started at 38/34 (front/rear) and rolled down the street. before i started moving i could tell the back tires have to much air in them and the fronts looked a little rounded too. after rolling about 3/4 block it was confirmed cuz nothing was rubbing off the outter inch of the front or rear tire.

just for the heck of it i dropped to 32/30 and to my surprise they looked better. rubbed them down again and rolled down the street. the chauk seemed to be coming off evenly and only about 1/2in of tread (on the in and outside) was not touched.

is 32/30 (front/rear) to low for general grabber at2s in a 255/70-16? i have never done the chuak thing before and i can honestly say i have never ran truck tires that low. did i miss something?

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295lb feet of torque, 2.5in DayStar lift, 255/70-16 General Grabber AT2s

Sounds like your doing it right.........................I used to run 30/25 psi in the 285/75/16s I had on my Z71 ,thats what it took to get even wear paterns on them. I don;t see a problem running that psi if that what the wear pattern shows it needs............not to mention they most likely ride better too Oh yea, I running 32/28 psi in my 245/70/16 BFGs right now

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'05 Bright Silver Sport CRD
245/70/16 BFG AT KOs (On the second set now.....First set was replaced at 106K miles)
some stereo stuff.........
L.O.S.T. #053490

thanks .... i just didnt seem right having so much wieght and so little pressure ..... oh well. it see bad wear then i'll change

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295lb feet of torque, 2.5in DayStar lift, 255/70-16 General Grabber AT2s

I am at 44 PSI, guess I will too will see how bad they wear.

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[iurl]http://home.comcast.net/~n3qik/Site/Welcome.html[/url]

wow

at 38 i could really tell they were ballooning up ..... what kind of tires do you have

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295lb feet of torque, 2.5in DayStar lift, 255/70-16 General Grabber AT2s

Stock tires.

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[iurl]http://home.comcast.net/~n3qik/Site/Welcome.html[/url]

There's a dramatic difference in stock tires and 255s...255s are having their sidewalls deflected inwards on stock wheels, causing the bowing you're seeing.

A second major difference is in the volume of air, and the amount of tire in contact with the road. PSI is literally Pounds per Square Inch...it is how much weight one square inch will support. Supporting more weight can thus be done in one of two different ways: increase pressure, or increase surface area. When you go to a bigger tire, you're increasing surface area, and thus can decrease pressure to support the same weight.

Most tire manufacturers have tire inflation charts that show how much PSI you need for a given weight. Basically, the inflation charts work out by taking max load and max inflation pressures, and calculating the ratio, figuring in your load, and voila. E.g.

Tire X in 255-70-16 has max load of 2000# at 40 psi max pressure. You weigh your jeep and determine that it weighs 2000# on a given axle. You have 2 tires on the axle, each one carrying 1000#. Optimal inflation would be 20psi (1/2 of the max, as it's carrying 1/2 of the weight).

Tire Y in 245/75/16 has a max load of 3000# at 80 psi. Your jeep weighs 3000# on one axle. Optimal inflation is thus 40 psi. If your jeep weighed 3500# on one axle, optimal inflation would be 47 psi.

Here are the important caveats:
1. You do not want to go below a certain minimum PSI for normal road use, even if your monster tires would allow it (I probably wouldn't go below 20psi).
2. If you increase load (i.e. hook up a trailer, load the jeep up, etc.), you must commensurately increase tire pressure.
3. Manufacturer inflation charts typically build in a bit of a fudge factor. In the first example, they might suggest 22-24 psi, rather than 20.

I'm not sure if we can cross-link to non-competitor BBS or not. If anyone wants to see great discussions of tire pressure, PM me and I'll point you in the right direction.

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2005 Jeep Liberty CRD, Provent CCR, 2.5" lift