Last edited by teotwaki; 12-18-2012 at 03:09 PM.
Trip reports are on my Blog: "Sun To The North"
Two Favorite Expo Quotes: "A bad day on the trail is better than a good day in the city" & "Bad days make for GREAT stories!"
My instinct would be to air down more in deep or soft sand if I needed to.
The rule I use for airing down any tire regardless of the weight it is supporting goes like this.
At highway pressure, and on a hard surface, measure the distance from the ground to the lower edge of the rim.
Say it's 8" for the sake of easy to understand math.
Now, start letting air out until you have reduced this distance by 25%, which in our case would put the rim 6" off the ground.
By doing this, you have now increased your foot print by 200%.
Airing down this way keeps me from "picking" a pressure and reducing to that, where actual tire contact is more important.
Meaning that one day I may have my right rear and left rear really close to the same pressure just by luck, and another day depending on my current load both tires could be different pressures but have the same sized contact patch.
So, in a nutshell it isn't the tire pressure that matters as much as the contact area. Reducing rim to ground distance at the same ratio for all tires regardless of supported weight on that tire will give optimal results.
You can certainly go more or less with this depending on your needs, but do them all the same way and don't pay attention to the pressures specifically as you will find each tire could easily have a different pressure.
How are you making the determination as to what tire pressure to run. I use chalk with the trailer loaded, make a line across tread, then roll it over a few revolutions and look at chalk line. With my trailer and weight I came up with 17 psi and I have good contact pattern and no wear problems. Do the same with Jeep, and on 35's my street pressure is 25 psi.
06 UNL RUBI Locked /Armor
4.5" LIFT/35's /4.88
07 AT CHASER
I just use the 4 psi rule. If after an hour of driving my tyre pressure has gone up by more than 4psi it has not enough air, if it hasn't shifted too much. You soon have an understanding of pressures for different circumstances and can then tweak from there
Are you referring to highway pressures?
I start with the recommended pressure on the door jam, and adjust from there with either chalk or just a narrow tread wide swipe from a soapy wet towel. It cleans the rubber good enough to see where the tire is contacting the road, or not. A paint pen works too.