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Found this on the Quadratec forum. It may have been seen before but I thought it was pretty helpfull for people who would like to try this?
Think its time to write this here in the tech tip section because I'm tired of writing it all the time in the tech section.
So you've got new tires, and they're bigger than the ones you took off so the factory recommended pressure printed on the door jam wont work. Neither will the max pressure stamped on the sidewall of the tire. Why not you ask? The max pressure is followed by a weight, that is the amount of weight that the tire can support safely at a given pressure. In most cases the entire weight of your jeep could be supported by one or two tires if inflated to max pressure, you don’t need that much. So, what to do?
I know, I'll post the question and see what everyone else is running and use that...
Wrong answer, thank you for playing, please have a seat and listen up.
Everyone’s rig is going to have a slightly different "optimal" pressure to get the best ride and tire wear. Even similar setups will have different weight distribution and options that affect how the tires wear. Joe TJ who has added nothing but a spacer lift and tires is going to need different pressures than John YJ who has added a V8 engine and one ton axles, even though they have the same sized tires and rims.
So how do you find out what’s right for you and your rig?
Well, it’s fairly easy, and only takes a little time. Allot about an hour to figure it out and make sure you have access to a compressed air source. Make sure you have everything in the jeep that you normally have in there, if you carry 100 lbs of tools to work, make sure to include them, etc. Do this with about 1/2 tank of gas.
You will need:
Chalk or paint pen, something that will make an easy to see line across the tread of your tire.
A road to drive on, preferably mostly strait, and dry.
A tire pressure gauge.
A source of compressed air to inflate tires.
Here’s how to figure it all out.
Draw a line across the tread of all 4 tires, which means sideways, from left to right.
Drive a bit, and stop to look at the lines you drew.
If the lines are wearing off in the center more than the edges, you have too much air. If the lines are wearing off on the edges more than the center, you don’t have enough air. 99 times out of 100, you'll have way too much air to begin with.
Let air out or add air depending on what the wear pattern of the lines told you, and repeat the process. The goal here is to have the lines wear completely evenly, while having as much pressure in the tires as possible.
Once you get even wear of the lines, check the pressure and record your readings. Don’t be surprised if the numbers are lower than you expected, and don’t be surprised if they are different front to back.
Just as an example of how low the numbers can be, I ran one setup that took 21psi front, and 19psi rear to get even tire wear. Ended up getting close to 50K miles out of those tires before I got rid of them to get a bigger set, they still had usable tread on them.
Now on to trail pressure. A good rule of thumb to follow is to use half of your normal road pressure, round down. If your running 19psi, air down to 9psi for the trail. Don’t be surprised if you loose a couple psi over the course of a weekend, as the tire will "burp" a bit from time to time as it pulls partially away from the rim when twisted, bound, or pulled by a rock or root. Adjust as necessary for the next wheelin trip, but don’t get carried away unless you or someone in your group has an air source. Different trails will require different pressures, so its personal preference once you leave the pavement.
This concludes this test of the emergency tech broadcasting system, we now return you to your regularly scheduled programming.
_________________
Richey
0IIIIII0
2006 IMPACT ORANGE RUBICON
305 Mt/Rs MT Classic II's
2.5 lift
1.25 JKS BL
JKS quicker Discos
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this should go in the tech section definitly it's a big help