Air Pressure???

EAGLE01_2002Libby · **Posted:** Thu Dec 16, 2010 9:57 pm

Okay, so i ran over a roofing nail somewhere and took it to Discount Tire and they fixed it for free...AWESOME!

Well...when the guy handed my my keys back he said my tires had WAYYYY too much air in them. He said they were at 70 PSI
I Literally said "I know, they are supposed to be at that, they are rated at 80 PSI."

Well he went on to argue that the tires that are rated at 80 PSI should really only be put at 35 PSI.
So he had all the air taken out before he gave me the keys.

Well, I just said forgert it ill figure that one out on my own...
Thats where i need help.

I need as much info as possible about tires, winter and summer

I have a set of 225/75/R16 Wild Spirits (10 ply, Load E, 80 PSI)

Help please.

I gotta say the ride home was really smooth :ROTFL:

67Customs · **Posted:** Thu Dec 16, 2010 10:00 pm

Open the driver door, look at the white sticker on the door jamb and see what the correct PSI should be. Keep them at that. Done.

My KJ says 34 PSI under normal load conditions.

tommudd · **Posted:** Thu Dec 16, 2010 10:06 pm

Does your KJ weigh 20,000 lbs if not why the H are you running that much air?
Way too much for sure, you have them at max which is not right !
34-36 should be a good average

SETexasLibby · **Posted:** Thu Dec 16, 2010 10:48 pm

you are seriously lucky you didn't blow out the tire when you ran over the nail considering the air pressure you were running.

Jeepjeepster · **Posted:** Thu Dec 16, 2010 11:51 pm

He is very much correct. Running the incorrect tire pressure isnt something to mess around with. Always run the tire pressure recommended for the Jeep.

Also, it scares me to think people inflate their tires to the MAX tire pressure on the side wall. Thats the MAAAXXXXX tire pressure, not the cold tire pressure. My tire pressures range from 32 to 39 depending on the temperature.

tjkj2002 · **Posted:** Fri Dec 17, 2010 12:01 am

Jeepjeepster wrote:

He is very much correct. Running the incorrect tire pressure isnt something to mess around with. Always run the tire pressure recommended for the Jeep.

Also, it scares me to think people inflate their tires to the MAX tire pressure on the side wall. Thats the MAAAXXXXX tire pressure, not the cold tire pressure. My tire pressures range from 32 to 39 depending on the temperature.

Actually if you look at the sidewalls that max psi listed is the max cold psi,say's right there on the tire,go look.Safety limits have been built into the tire to go past the cold max when the tire is warmed up.

With a "E" rated tire on a stock KJ about 36-38psi is just about right,fully armored KJ would be about 38-42psi.

Draco · **Posted:** Fri Dec 17, 2010 12:35 am

One thing to be aware of is that the air pressure needs to be matched to the weight of the load, and not simply the tire.

Suppose that your grandmother/next-door-neighbor/boss wants a four-wheel-drive loader for Christmas.

That could weight 20,000 lbs. So for your trailer, you're going to need some load range E tires and you're going to need to run them at a high pressure. I'm joking around to make a point. Those load range E tires really are designed to carry heavy loads.

If on the other hand you take those same load range E tires and put them on your 4,000 lb (?) Liberty, then you're not going to run the same high pressure. The load range E tires are popular for off-roading because they also have a high puncture resistence due to all the plies and extra rubber. But if you run them at their full rated pressure, they're going to be WAY too stiff.

I'm currently running around 35 psi with load range E's. Until recently I was running about 40 psi but decided I liked the lower pressure better on some of the roads I drive daily.

audiboy86 · **Posted:** Fri Dec 17, 2010 12:45 am

Thank yall for clearing that up because i have a good bit of wieght on mine so i have been running them aroun 50 to 52 but now i see that was way off. I am not fully armored but will be shortly and ussually carry about 500 lbs in tools almost everyday of the week. I have Cooper ST 265/70/17 E-load range of course. I am going to let some pressure out tomorrow to probably closer to 40.

JeepinJarhead03 · **Posted:** Fri Dec 17, 2010 1:18 am

I usually chalk or wet roll them till they pattern flat and it's usually dead on within a psi or two of what it should be, i'd imagine at 80 at that load they were patterning about 2-3" of rubber

tommudd · **Posted:** Fri Dec 17, 2010 1:57 am

Would leave a track that looked like 2 motorcycles went down the road :lol:

ATXKJ · **Posted:** Fri Dec 17, 2010 8:16 am

If it's an LT - it needs more air pressure than P rated tires

http://www.nittotire.com/assets/safety/Replacing%20Tires%20on%20Light%20Trucks.pdf

otherwise the sidewalls flex and the tire overheats

tommudd · **Posted:** Fri Dec 17, 2010 8:28 am

But again they are talking about MAX LOADS , not normal every day driving

Draco · **Posted:** Fri Dec 17, 2010 12:31 pm

JeepinJarhead03 wrote:

I usually chalk or wet roll them till they pattern flat and it's usually dead on within a psi or two of what it should be, i'd imagine at 80 at that load they were patterning about 2-3" of rubber

That's a really good idea. Here's a picture to illustrate what he means:

So when the tire is over-inflated ("high pressure" in the figure), there is a very small contact patch at the center and the traction is going to be poor! As tommudd so nicely put it, that small contact patch will leave a skinny trail, like a motorcycle tire.

EAGLE01_2002Libby · **Posted:** Sun Dec 19, 2010 2:49 pm

Yea i understand that the tires should roll flat, the tread should evenly make contact with the ground. But with it at 70 Psi it makes even contact. with the 35 or so that he put in, it does not.

tommudd · **Posted:** Sun Dec 19, 2010 2:56 pm

How do you figure that at 70 it has full contact and at 35 it does not?
Unless you have an extra 3000-4000 lb in the KJ 70 lb is just way too much
If you could see a real picture of the contact area it may be the size of a cup for example where as at 35 it would b more the size of a plate ( just an example but to put it in terms most can see in their minds )

JL Rockies · **Posted:** Mon Dec 20, 2010 2:40 am

This isn't the craziest thread I've read on here... but it's close.

tommudd · **Posted:** Mon Dec 20, 2010 9:20 am

real close

SavageUrge · **Posted:** Mon Dec 20, 2010 9:38 am

In all my years, I've never paid attention to the sticker on the door after replacing the stock tires with something different. I strictly go by the sidewall of the tire and inflate it to within 5 psi of maximum. This has always worked for me just fine.

Matt_ · **Posted:** Mon Dec 20, 2010 10:12 am

Wow. Now I come from the full size truck world where its hard enough convincing guys with 1500 series trucks that those E rated Max pressures are for 3500 series trucks with a 4000lb load in the bed...... I never thought I'd see guys with small/mid sized SUVs trying to run Max pressure. That's actually on the verge of dangerous given that braking distance is directly related to you contact patch.

35psi is good for a kj and kk. If you have a bunch of armor/tools/etc then 40ish is good too. 50 is too much... if you need that much pressure in one of these vehicles then you're overloaded.

There's not enough weight in a fully loaded liberty to cause an E rated tire to flex & overheat at 35-40 psi. That's more of a concern for 1500 series trucks hauling Max capacity; and even then, 50psi often more than makes up for the equivalent load published for the stock p-rated tires at 35 psi.

LibertyCRD · **Posted:** Mon Dec 20, 2010 12:48 pm

Matt_ wrote:

:ROTFL:

Wow. Now I come from the full size truck world where its hard enough convincing guys with 1500 series trucks that those E rated Max pressures are for 3500 series trucks with a 4000lb load in the bed...... I never thought I'd see guys with small/mid sized SUVs trying to run Max pressure. That's actually on the verge of dangerous given that braking distance is directly related to you contact patch.

35psi is good for a kj and kk. If you have a bunch of armor/tools/etc then 40ish is good too. 50 is too much... if you need that much pressure in one of these vehicles then you're overloaded.

There's not enough weight in a fully loaded liberty to cause an E rated tire to flex & overheat at 35-40 psi. That's more of a concern for 1500 series trucks hauling Max capacity; and even then, 50psi often more than makes up for the equivalent load published for the stock p-rated tires at 35 psi.

Exactly. That's what I've been trying to tell these clowns for a year now, and nobody listens. If the guys with Ram 1500s don't want "E" rated tires, why on God's green Earth does somebody with a compact Jeep think they need them? All it does is suck your fuel economy, ride rougher, and add unsprung weight. You'll NEVER put a load on a Jeep that will need an "E" rated tire. Ever.

And yes... the PSI on the tire is the MAX you can put in it... it is NOT a recommendation. Geez people... :shock:

Air Pressure???

Who is online