NEWS PARTS JEEP & 4x4 ATV & UTV

tire pressure

961 Views 10 Replies 7 Participants Last post by RRich, Nov 19, 2003

2584

Discussion Starter · Nov 18, 2003

hey ya'll,
just a quick question about tire pressure.
I'm running 265/15's right now and when they were new I ran 35 psi as per tire specs. and the front tires have wore even, but the back set wore down in the center of the tires, so I dropped the front down to 28 psi ( still wearing even ), and the back down to 20 psi and they ( the rear ) started to even out on the wear pattern. I'm fixin' to buy a set of Maxxis Buckshot mudders in a 33/12.50/15 and was wondering if anybody had any similar wear problems or suggestion's as to tire pressure to make them last. The tire man where I bought them said that the Jeeps are real light in the rear end and litterally skip down the highway, causing tire wear on the rear , unless you run the rears at a low pressure. Any suggestion's? Thanks.

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1060

· #2 · Nov 18, 2003

I run a 2-4 psi difference between the front and rear of my Jeep. Front 26-28/rear 24-26. But thats with 35" mud T/A`s. I also keep a close watch on the pressure, usually check once or twice a week. Never had any wear problems. I also rotate every 3-5000 miles. The Buckshots are a good off-road tire, but I haven`t seen a set yet that was any good on the road, they all ride like crap.

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WILL

· #3 · Nov 18, 2003

In reply to:

The tire man where I bought them said that the Jeeps are real light in the rear end and litterally skip down the highway, causing tire wear on the rear , unless you run the rears at a low pressure.

[/ QUOTE ]

He doesn't have much experience with jeeps then. Dirt Dog weighed his jeep a couple years ago and his was Front: 1680 lbs......Rear 1820 lbs....Total 3500 lbs. I weighed mine around that time too and it was Front: 2120 lbs......Rear 2080 lbs....Total 4200 lbs.

Point is, the jeeps drivetrain is centered enough between the axles that the front/rear balance is pretty close. The same tire pressure should be fine for front and rear. Just rotate your tires.

Here's the thread.

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027

· #4 · Nov 18, 2003

I have been running 33x12.50s for years and I always run 28psi in them on the road they wear very well and even. just rotate ever so often.

Yep my Jepp weighs about 4300 and that is pretty much even front to rear. Now thats with a hard top.

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· #5 · Nov 18, 2003

I'm the same as 4x401cj5. My jeep may be a bit lighter.

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1245

· #6 · Nov 18, 2003

I run about 20 in the front and rear. The jeep weighs about half the capacity of the tires, so I figure I can run half the pressure. Any one disagree?

Seems like my tires say 2000 lbs at 36 PSI

2000x4=8000. Jeep weighs about 4000 - 50%

36x.5= 18 lbs

I should be safe at 20 lbs?

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WILL

· #7 · Nov 18, 2003

I run my 33x12.50's at 20psi also.

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jfralph

· #8 · Nov 18, 2003

This subject has been discussed to death. Even so, I see those that are still uninformed. Just because a tire lists a weight at a certian pressure, dosn't mean half the weight is half the pressure! Contact your tire dealer, and get a weight vs. pressure chart for your tires. Then use it as a starting point.

Then, as explained on here many times, place a heavy chalk mark on your tires and drive straight with the jeep. If the chalk wears out on the edges faster, Add some air. If it wears in the middle first, reduce pressure. Keep doing it until you get even chalk wear.

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027

· #9 · Nov 18, 2003

In reply to:

place a heavy chalk mark on your tires and drive straight with the jeep. If the chalk wears out on the edges faster, Add some air. If it wears in the middle first, reduce pressure. Keep doing it until you get even chalk wear

[/ QUOTE ]

Yep,,, There you go!! Thats how I arrived at 28 psi on my tires

In reply to:

Contact your tire dealer, and get a weight vs. pressure chart for your tires.

[/ QUOTE ]

Hmmmm,,, there is a little more involed than that,

, but that is as good a place as any to start

for a passenger tire. When you get into load rated tires thats a whole new game and other things need to be taken into consideration, even when using load specific rated tires for trucks on Jeeps

this will take in side wall strength and deflection at varing psi's but thats a whole nother thread

Click to expand...

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jfralph

· #10 · Nov 19, 2003

Gp'n:

You have me totaly confused. What does all the BS your spouting have to do with proper inflation.

What proper inflation does is allow an even pressure across the tread. To much pressure, i.e. a tire with 50 psi in it for example, and 1100#'s of jeep on top of it, only needs/causes 22 sq inches of tire contact. Since the tread width on a 33x12.5 tire is 10-12", less than 2 inches of running length will contact. Since tire dynamics will not allow that, the tire tends to get an oval shaped contact patch in the center of the tire. Thus, wearing out the center of the tire. The tire manufacturers have figured out the optimum shape/contact patch for their tires. Optimally, they want that contact patch for safety, durability, and longevity. They know what tire pressure at each loading will cause that contact patch. Thus they develop tables to assist customers in achieving the proper inflation. Now, you throw in the variables of load, temperature, wheel width, speed, and a host of other factors, and yes, the manufactures tables are still valid, however, a little tweaking may be called for. Thats why the chalk test is so valid. If, however, you cannot do a chalk test, and stay with the manufactures pressure, you will be fine and only marginally compromise optimum tire characteristics.

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RRich

· #11 · Nov 19, 2003

Yeah - but --

When you consider the cosine of the cross sectional area divided by the weight, then multiply that by the pressure times the number on the color chart --???////

The chalk test - or a little line of paint across the tread - will tell you exactly how the tire is wearing and contacting the ground - real world vs theorey.
You may want to tweak it slightly depending on how it handles - if it feel too "draggy" add a couple pounds.
Do all 4 corners - they won't be the same.

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