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Tire Pressure???

sherpamike

NAXJA Forum User
Does anyone know what the recommended tire pressure is for 31X10.5" Goodyear MT/R's? On the sidewall it says the max. pres. is 50psi. I don't think that means to run the tire at maximum. Does it?

While I am on the subject, how far is everyone airing down when they get into the sand or on the rocks? I am not too extreme and don't have or need beadlocks. How far down can I go without losing a tire? Thanks for your help!
mike
 
sherpamike said:
Does anyone know what the recommended tire pressure is for 31X10.5" Goodyear MT/R's? On the sidewall it says the max. pres. is 50psi. I don't think that means to run the tire at maximum. Does it?

While I am on the subject, how far is everyone airing down when they get into the sand or on the rocks? I am not too extreme and don't have or need beadlocks. How far down can I go without losing a tire? Thanks for your help!
mike

I think I'll get the 'super-poster-of-the-day-award' but I usually run my 35" MTR's on 10" wheels at 27 lbs on the street. I had a set of 32"on 7" wheels and I ran them at 29 lbs.

I ran the 32" as low as 7 lbs of pressure (being on a 7" wheel probably helped) and never totally blew a bead--had some times that air was escaping, though. The 35" tires I ran at 7, but as they broke in, I started losing axles quite regularly. I now run the front at 11-12 psi and the rear about 10 and like that.
 
On the street you should find a sweet spot somewhere between 28-33 psi, it all depends on how hard you can stand it and how much gas you want to buy.

On the trail you should be good at 12 psi.
 
The factory pressure for stock 225s is 30 psi. Larger tires need less pressure, and actually want less pressure to keep the tread flat on the pavement, especially if running a wider tire on a stock width rim. However, you don't want to run so low that heat buildup becomes an issue -- remember the Ford Explorer/Firestone tire flap.

I run 31s on stock rims on my MJ. I run 28 psi and the tires are wearing faster in the center of the tread, which means that to maximize tread lift I should drop another couple/few pounds.
 
Eagle said:
The factory pressure for stock 225s is 30 psi. Larger tires need less pressure, and actually want less pressure to keep the tread flat on the pavement, especially if running a wider tire on a stock width rim. However, you don't want to run so low that heat buildup becomes an issue -- remember the Ford Explorer/Firestone tire flap.

I run 31s on stock rims on my MJ. I run 28 psi and the tires are wearing faster in the center of the tread, which means that to maximize tread lift I should drop another couple/few pounds.


I think Eagle hit the key.....watch your tread wear. If it wears in the middle, you're running too much air pressure. If it wears on the 'shoulders', you are running to little.

Run a piece of sidewalk chalk across the surface of the tread and drive about 30-50 yards and check the 'wear' on the chalk to get you dialed in.
 
I've always run 32 to 35 psi in a/t's and m/t's from 31" to 35" and have always had great tread life success under "normal" driving conditions with adjustments for load, etc. Might be a little less cushy on the tushy, but hey they're 4x4's. Best advice, like given above, is just be observant of tread wear. YMMV.

I run 10 to 15 psi on the trail... depending on the trail.
 
To get the correst tyre pressure there are a few factors involved. One to remember is that it is the air volume and not the pressure that supports the weight, so to get the same amount of air in a small tyre will require more force and therefore pressure than the same amount in a larger tyre. i.e.. 35 psi in a 30"x9.50" tyre may have the same amount of air in it as a 33"x12.50" with 30 psi. I used to have a lot of punctures on my outback trips from stones getting forced into the tyre casing through the sips, (the cuts that are put in the tread blocks). It turns out that having too much pressure opens up the sips and makes it easier to get the stones in. After 7 punctures on that trip and finding that the centre of the tyres had worn I knew that I had to find a better way of getting the right pressures. As it always happens after the fact, I read in a 4x4 mag after I got back that to find the right pressures for different temperatures, loads and conditions you take front and rear pressures cold, and then again immediately after at least 20 minutes at highway speeds or more and there should be a 4 psi increase. If there is more than 4 psi, than you had too little to start with and if there is less than 4 psi, than you had too much. I have used this technic for the last 5 years and didn't suffer one puncture from stones again, (had a steel railway spike go through the trailer tyre on the old Ghan railway line) on the same roads, temperature and loads. The tyres have also lasted longer with very even wear. You can use this technique for your trailer as well. For my tyre size (275x70x16) and load, I run 33 psi in the front and 32 psi in the rear. My mate in his XJ ended up with 35psi front and rear with 30"x9.5"x15 's and later with 33 psi front and rear with 31"x10.5"x15 's. I ended up with less in the rear because I don't carry much in the back of the car, most of it is in my trailer.
 
I kind of skimmed through all the replies so I might be doubling something up but hey.... it's all good :)

ANyways the info on the side of tire says what's the MAX pressure for it, not what you should run it at! I always fight with the trie people after roation as they fill me up and I get a "ping pong ball" ride home in my XJ.....

Anyways, find a flat piece of road (street around the corner.. .what have you). Take a piece of chalk and draw a THICK line across each tire. Then drive around the block and look at the lines. If the lines are evenly worn, you're good. If outsides are worn out more add air... if insides are worn out more reduce pressure..... At the end you will end up with the optimum pressure for tires (I'd then add the two fronts and divide by two to get what I'd run.. and they should be pretty close to each other anyways, and then do the same to rear).

Oh remember to redo it when you load up for a big trip as weight changes pressure requirements.

Kejtar
 
The chalk meathod is very helpful, but also just make sure to keep in mind your particular tire type or construction. Some of the M/T's being built now have the agressive outer lugs slopped away from the center of the tire just enough to keep them from slapping the pavement to help reduce noise (which also reduces wear). While on pavement the truck runs more on the narrower quieter center tread pattern and when offroad the lugs can dig in like we need them to.

The chalk on your tires can also be showing you alignment issues.
 
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