Tire Pressure (33's)

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jeepndogs said:
The way the OEM’s come up with the PSI rating on the doors is by using a formula. Max weight of tire listed x 4= x. X / curb weight = x. Max PSI listed on tire / x= suggested PSI

So sidewall max weight = 2250 x 4 = 9000
9000 / 4000 ( weight of Jeep) = 2.5
Max psi listed 55psi / 2.5= 22 psi recommend for Jeep.

Is you call most if not all tire companies and ask them how much psi to run they will ask weight of vehicle and use this formula. If I can find it I will actually post a file Cooper sent me on SST pros.
Click to expand...
I know this is a few weeks back, but I have a question on this formula. I run Cooper STT Pro 33x12.5r15 tires (load range C 108Q). The max sidewall weight @35psi is 2205 and my Jeep weighs 3580lbs. When I put these numbers in I get the following, which can't be correct:

2205 x 4 = 8820
8820 / 3580 = 2.464
35psi / 2.464 = 14.204 psi

What am I doing wrong? I think it's probably in the max tire pressure value of 35psi, but I can't find any other number than that for max tire pressure.
 
Hi jeepndogs,

Thanks for your input. Using your formula I came up with 17 lbs !!
I'm running Yokohama Geolander A/T-S 33"x 12.50-15" on the stock 15"x 8" Canyon rims.
My sidewall max is 2205 @ 35 lbs. The Vin sticker shows the standard tire pressure @ 29 lbs all around.
So......2205*4 = 8,820.
8,820 / 4450 = 1.9820224719101123595505617977528
max listed psi is 35 lbs / 1.9820224719101123595505617977528 = 17.658.......lbs

Am I doing this correctly?
 
The formulas will will drive you batty looking for the "correct" answer. There isn't one. Any formula will be inadequate because the optimum pressure will depend upon many factors including the construction of the particular tire, the weight of your rig, how and where you drive it, and personal preference.

For 33" "flotation" tires (i.e., 33x12.50R15LT), start at about 24 psi and experiment. 24-26 psi is usually right for a CJ, YJ or TJ depending upon the particular tire and the weight of the rig. My TJ Unlimited (LJ) is a bit heavier so I run my "metric 35's" at 26 psi around town and 28 on long Interstate runs.

You might try the "chalk test" with a piece of sidewalk chalk to help zero in on a particular psi, but bear in mind that the chalk is just a visual aid to make it easier to see how the tire tread contacts the ground when going a short distance in a straight line at low speed on smooth pavement. The chalk test cannot provide precise results or measure the contact patch at speed or in a turn but it is a place to start. Try it at 24 psi and go up in increments, then pick the psi with the pattern that looks best to you.
 
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