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I have 32x11.5 50R15 tires on my Samurai. What is the proper inflation pressure for on road and off road use?
 

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Usually it's marked on the side of the tire for proper inflation on the road.
I have 31x10s and run 10pounds off road.
NO.
Sorry bud, but you are wrong there. The pressure listed on the side of the tire is the maximum inflation preassure that the tire is designed for. It does nt take into consideration the type and/or weight of the vehicle it is bolted onto. If you run that pressure on a zook, it will ride like a paint shaker.

Start with the pressure listed on the data plate on the side of the dash board. It should say 20 psi (22 for the rear if you are loaded). Some of us have stock rigs and the pressure is pretty close for regular driving on average tires. Some of us have added heavy bumpers, roll cages, gas cans, etc. that would change the pressure put on the tires. Some tire types/brands have heavier sidewalls that change how low you can go.

Start with 20psi.
Drive through water and then then dry road and check your footprint. If the footprint is the full wifth of the tread, and it is clearly the same across the tread pattern then you are right on target. If the print is skinnier than the actual tread width then there is too much air in the tires. If the print mark is lighter in the middle, then you have too little air pressure, so bump it up a little.

There are other, more technical ways to check, but this is the easiest, most basic way.

For offroad, all bets are off as there are many other factors. Less air pressure leaves a larger footprint which equals more traction, less disturbance of the trail (makes the environmentalists happy while getting you farther down the trail!). But if you go too low you can lose a bead or slice a sidewall (most street tires have thin sidewalls). Here are some pressures I have used:

Stret tires - anything that you would put on a normal road sedan
street tire / on road - 20psi
street tire / off road - 15psi (but be carefull of the sharp stuff)

Offroad tire - All terrian or Mud terrain tire
Offroad tire / on road - 16-18psi
Offroad tire / off road - 10-12psi depending on wheel/tire width ratio

extreme tire - Something built for extreme wheeling like a Swamper SX or Swamper Bogger
extreme tire / on road - 12-16psi
extreme tire / off road - 4-6psi

When I ran 32/10.50 Swamper SX's on 8" rims I could air down to 4psi and run the trals all day without a problem.
Now I run 33/12.50 Swamper TLS Radials on 8" rims and I only go down to about 8psi on the same trails. (thinner sidewall)

*note* if you run beadlocks you can go even lower on the trail and not worry about losing a bead. But most beadlocks are also illegal to use on public roadways in most states...
 

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I have 32x11.5 50R15 tires on my Samurai. What is the proper inflation pressure for on road and off road use?
Read the plate on the side of the dash; start there and go DOWN. The pressure listed there is for stock 205 tires, and yours are _MUCH_ larger, and so need less pressure to get a flat footprint on asphalt. Off-road, you can "air down" to 8-12 psi (mebbe even lower) if you use a rim width specified (wide enough) for the tire, so the tire bead doesn't come off the rim easily. It's a bit tough on sidewalls, so use good judgement and keep your speeds down (until you "air-up" again). I run the BFG TA/KO (3-ply sidewall) and use pressures about like BillJohn suggests.
 

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Discussion Starter #5 (Edited)
Good advice guys. Thanks for the tips! I took a guess at 20 PSI and have them at that now. I'll do the water print test and see what it looks like.

The tires on it now are 32" Pro Comp Mud Terrain M+S. Anyone know where that falls on the scale of crap to good for tires? Will be used mainly offroad except for the highway drive to reach the trails.
 

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good mud terrain tire for moderate off road and still streetable without a lot of screaming. They have a 2 ply nylon wall though so don't air them down like you would a 3 ply steel belted wall.
 

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easiest way to find an accurate pressure is to ask your local tyre specialist, say your vehicle weight, the type of tyre, and the tyre features such as size and width.;)
 

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wow... my tyre dealer told me around 30-35psi for BFG a/t, size 215/75R15... its softer at lower pressures, but i also find it feels like theres more weight in the car.
 

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30-35psi may not quite feel right, but if you over inflate it, the tyre goes bald in the middle, under inflate it, the tyre goes bald on the outsides for most on road cars, and if youre going 4wding, you need as much tread as you can so this may be a case of experimentation, if the tyre pressure doesnt feel right, change it until it does feel right:):) but still keep an eye on where the tread is wearing on the tyre, if you're going to get another set of the same tyres. if i remember right, when i ran 32"s i was told about 30psi for road use
 

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i want to go 31's but my sidesteps limit me to about 29, maybe 30... id take them off but they look awesome...

back to the wear issue... its hard to tell where theyre wearing the most, i only just got the swivel housing fixed which was throwing out all the front... it probably is a bit high after hearing what everyone else runs, especially considering i dont have bullbars, etc, and i occasionally have one passenger, once a month maybe have back seats in for 3 passengers...
should make time to do that water test... oh, and ive run my tires at as low as 6-7 psi, at a crawl pace just to get out of sand... obviously reinflated asap.
 

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bout time for a lift then mate :) maybe lift it around 2-4 inchs, that will give you good clearance for your tyres so that they dont rub, the first tyre upgrade that went on mine, was a set of self-made 3 inch lifted shackles, and then a set of cheapo 31s, since then its gone to 33s (the picture is when i first bought the car :p)
 
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