I've got to agree with OnTheHunt on that one. For giggles, I asked myself at 3 different tire shops. All three said it is WORSE to run a tire underpressured, than at the max pressure. Also, they all said that the tire is designed to carry "up to" the weight stamped on the sidewall... But they were designed to operate optimally at ANY loading up to that maximum and not wear unevenly, when pressured to the sidewall max. The danger is when you lower the pressure below the sidewall max, you also lower the carrying capacity to an unknown number, and there is a very real chance of your tire's new "safe capacity" at that lower pressure being below the weight riding on it.

Make life simple on yourselves - You KNOW the weight of your vehicle. You can estimate the weight of your cargo. If those numbers (split 60/40 for the distribution of weight) are close to the number stamped on the side of the tire... You need to be running at full pressure to be safe. But when you are only running empty... Using the full sidewall max will not only keep you prepared for any change in load (stopping at the store on the way home?) but will give you better mileage without costing you any adverse wear.

This is crazy
I can not belive that ANY one would think that running a 10 ply tire rated to carry 3000+ # at 80psi
would put 80psi in that same tire on a 4000# jeep
the math is jut not there
you need to run 1/3 that psi to get good tread life and good ride

Now I know some one will want to argue so here are my credentials
he is in the other room ,younger brother mechanic trained in the army and has SEVERAL certification after that
also my self ,I am in the industrial weighing and measuring industry
I know what it takes to hold what load under any situation
I also am the guy who makes sure that the company trucks are in good working order
several 1/2 ,3/4 & 1 ton trucks as well as a VERY large truck ,56,000#
trust me the only trucks that get MAX PSI are the 3/4 & 1 tons that are at times breaking 10,000# on 4 tires
we get 50K out of a set of tires with no tread seperation and even wear
I also know that if I inflate the MTR's on my KJ to 80 psi the center will pop out
I could blow the valve stem off ,had that happen a few times to the trucks when the stems get old
but the one thing that is being missed is that the rim may not be rated for that kind of pressure
I know this because the steelies that come stock on the F250 have 85psi max stamped on them

If you have a tire guy telling you that it is OK to run your tires at 80psi he is trying to sell you new tires in a year or so
even 50 is to high for a KJ
more proof to come as soon as I get it scaned in or I find it on the web

link to safecar.gov
http://www.safercar.gov/tires/pages/TPa ... gUnder.htm

another good one
this one includes some ford/firestone issues
http://en.allexperts.com/q/Tires-2359/Tires-PSI.htm


and for fun take the tire test
http://www.safercar.gov/tires/Non-inter ... ntent.html

Jason, how wide are those MTR tires? Are they Load Range E tires in an 215/85 width/height? Are they even all steel belts on the tread surface? As I have stated, my tires ride SQUARE on the road. They are all STEEL on the tread surface, and at the rated pressure of the tire, ride just fine. I do not see any center wear, nor do I see the tires "bulging out" at the center of the tread. Modern tires are NOT like a balloon. They have structure which forces them into a specific shape within a certain air volume, regardless of the loading heaped on them. The trade off is in ride stiffness, yes. However, I would gladly trade a moderately stiffer ride (and firmer handling) in exchange for avoiding an overheating tire and a peel-off.

You claim to maintain a number of vehicles. Good for you. Have you actually done any empirical testing with any of those vehicles, or are you taking the numbers provided by the vehicle manufacturers only, because your job depends on it? Has your boss told you that you can test things to potentially save the company money?

Doubtful. I HAVE done my own testing, as well as asking for opinions. What I have found is by and large, the opinions are based solely on what their brother's uncle's cousin heard from a guy who knew a girl that had her car worked on by somebody smart.

So not based on any actual testing. The other thing to remember is that car makers are NOT in the business of selling long-lasting tires, OR in the business of caring how well those tires wear in any application. They want to provide a "Smooth car-like ride" on every TRUCK they sell, and so what if the BUYER needs to replace tires every 20k miles... They are getting a smooth soft ride!

The tire placards in vehicles are written based on the car manufacturers tests with a specific brand and model of tire that they plan on selling WITH the car. After that, if you change to a different size, brand, or sometimes even a different model from the same brand... You are off the reservation and on your own. At that point, the car maker's numbers may or may not put you SERIOUSLY into danger of death.

You want me to run an 80 PSI tire at 24 PSI? (That is exactly 30% as you stated above by the way) If I did, that would potentially lower the max weight rating of the tire to 870lbs instead of the 2900lbs it is rated for. (IF it were a linear regression, which it is NOT) I'm doing the math right in front of you and everyone else, and starting to seriously doubt your credentials. I hope none of your work trucks is treated like this, or those guys are in real danger.

The existing stock PASSENGER CAR tires that Goodyear supplied to Jeep and were installed on the KJ are rated at 1900lbs each, at a max of 35psi. The pressure isn't based on the weight, it's based on the tire's ultimate capacity AND on the materials the tire is made from. Those have the softest sidewalls I have ever felt, honestly.

Sidewall flex generates heat, just like folding a piece of plastic between your fingers makes it warm, before it breaks. Same thing here. But with a piece of plastic, you don't risk a high-speed peel-off and possibly flipping your car and dying. Full pressure prevents much of that flex, and protects the tire so it can perform as the TIRE MAKER designed. Lawyers and the threat of lawsuits force the companies to mostly defer to the car maker's numbers, but if you tell the tire company that you have installed significantly different tires than the stock sizes... (Anyone here with 245/xx or wider?) Then you are AGAIN on your own.

It's not about the wear or lack of wear that they will stop talking to you... It's about the threat of lawsuits if the tire maker makes ANY kind of pressure suggestion and they happen to be wrong.

I'm off the reservation with my size, b/c the KJ was never sold with 215/85 commercial highway tires in load range E. So I need to use my own testing and experience which tells me: run them at the pressure they are designed to carry the most at, and they can easily carry a lesser load without failure.

If you needed to lift a 200lb block of granite, would you ask Andre the Giant to help you, or David Spade? It would be easily within Andre's capabilities, and totally beyond David. (apologies to David Spade)

YMMV

geordi
I am not going to argue with any further as you have your OPINION on this matter and are stating it as fact
I have posted links to 2 different sources that state what other have already told you
If you want to prove us wrong and you right do what I did post your proof
you are stating OPINION NOT FACT
what I posted was FACT
I want you to post some thing that shows I am wrong

Now as far as my maintaing several trucks YES I do
I do not feel the need to "experiment" with these trucks they all carry about the same load all the time +/- 1000 LBS
so we simply keep the rear tires at max to carry the max load
the fronts are kept at about 60 psi

Now on to those
"all STEEL" tires
they are nothing more than a LT tire with a load range E
built the same as my MTR's
as you know I MUST keep good quality tires n our trucks ,my job and my LIFE depend on it
I push my truck to 10,000# gross wich is 2.5X your KJ
I run Bridgestone Deuler AT Revos on mine with a 10 ply rating and 3200 or so # cap at 80 psi
these are no different then what you have trust me
If what you have is so great then post up thee MFG and model so I can look into them

I hope that no one who reads this belives that they should run their tires at max psi

...as opposed to basing everything on a lawsuit. First it was said ALL the evidence came from the lawsuit (you even stated that you had to reiterate it 3 times to toddmudd). Now its ALL from empirical testing and asking those in the know. I'm confused.


Max pressure is just a guidline of what not to go above...its not the pressure you are supposed to inflate tires too under most any circumstance, nor is 90% of that. I still want to see an article, a test, some link or proof where this can be definitively proven. I can't find that anywhere...and its doubtful anyone can....but I am willing to concede and eat a big ol crow pie if its there somewhere.

_________________
2003 Silver Sport - Debadged
245/75/R16 DuraTracs
Cragar Soft 8s
OME Coils & Front Shocks, Bilstein Rear Shocks - Muddified Lift
JBA 4.5 UCA
K&N CAI
MagnaFlow Exhaust
Rola Vortex Rack

http://www.fusion-multimedia.com

I don't know if you know this, but ALL Wranglers, regardless of whether they came with a 225/75-15 Goodyear Wrangler GS-C or a 245/75-16 10 ply MT/R says 33 psi on the placard. Go look at ANY late-ish model Jeep...a ZJ, XJ, WJ, KJ, XK, WK, KK, JK...et al. they'll all say 33 psi. Even the '07+ Rubicons with the monstrous 10 ply BFG MT's, regardless of whether it's an unlimited or not.

To say that the company did any REAL testing, considering how different the tires all of those vehicles came with are, is ignorant, but to use the MAXIMUM as a guideline is just stupid.

my MT/R's feel stiff and unforgiving at 33psi. I don't know what you're smoking running a skinny-ass 10 ply on a Liberty. You even said it did well in mud. Puff puff pass, mein freund!

this whole thing is getting to the point of ridiculous, my Grandfather always told me to never argue with a pig, you get upset and the pig....well the pig just never understands....some people no matter how wrong will never admit that they know nothing about what they speak.

Tom

_________________
MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

quoted for truth.

Speaking of flowers....

I was in the tire shop yesterday talking to the dude about getting 245/75/16s in 10ply. He was very insistant that I wanted to get the 255/70/16s which came in 6ply (and of course are $75 more) due to the load I'd be putting on them. He said he would not want to put the 10 ply on my jeep. The confusing thing is that the rubicon wranglers came with 10ply 245/75/16s as stated above and are very close in weight to the libby. Is a 10 ply really just fine to run on the libby or should I blow an extra $50-$75 per for a 6ply?

Thanks!!!!
-Nick

_________________
'02 limited w/ stuff

10 plies are overkill, for the most part, I like my MT/R's, but I wouldn't have bought them if I didn't get a DEAL on them.

I'm assuming you're talking about BFG All Terrains? $75 a tire more would be the dealbreaker for me, since the 255/70 6 plies aren't gonna be any lighter than the 245/75s

tom...I like your pig anecdote

I don't like the pig anecdote - sounds too much like your insulting people who disagree with you just because they disagree.
the may not have been the intent - but that's how it comes across.


FYI - I run MTR's and don't have any problem with 10 ply tires - they're overkill for a Jeep - but they're great when you air them down in MOAB.

let's look at the positive and negative of high tire pressure.
Positive - at max air pressure - you will have minimal sidewall flex - almost none - so minimal sidewall heating - and virtually no chance of lamination. - You may have better traction in some slippery situations. and you will probably get much better mileage.

negatives - you should have increased center of tire wear - geordi said none - that doesn't seem to match the physics involved - it may not be noticeable without careful measurement, but that's a financial issue, his choice.

you will definitely decrease the tire contact area (that's what gets better mileage)
for 33 psi - you have 1 square inch of rubber on the road for every 33 lbs of Jeep. at 80 psi you have 1 square inch of rubber on the road for every 80 lbs of Jeep. laws of physics.
so what does that translate to?

for a 4000 lb vehicle - using the manufacturer recommended 33psi - you have 121 sq inches of rubber on the road, about 30 sq inches per tire.

at 80 psi - you have 50 sq inches of rubber on the road - about 12.5 per tire.

now tire pressure does not change the tire/road adhesion - that's a function of the chemical compound of the tire. the surface texture of the road.

so in an emergency situation - at the limit of tire adhesion - geordi has less than 1/2 the rubber on the road to stop his vehicle - therefore his emergency braking distance will be more than twice as long.

_________________
2005 CRD
stuff
Skeptic quod gratis asseritur, gratis negatur

If you have BFG tires read this under Inflation
thank you
http://www.bfgoodrichtires.com/bfgapp/s ... archResult

linky no worky like this
type in Proper inflation and the answer is there ,second line
or just read this ,same thing


Cold inflation pressure: The amount of air pressure in a tire, measured in pounds per square inch (psi) before a tire has built up heat from driving.

Inflation: Air is to your tire as oil is to the engine. Air pressure affects your vehicle's handling, traction, and gas mileage, as well as the longevity of the tires. We recommend that you check your tires about once a month and before any long trip. The accurate pressure for your vehicle can be found in the vehicle's owner's manual and often on a placard located in the vehicle's doorjamb.

Expand Glossary Results

I just noticed he's running 80 psi in these tires with his TPMS sensors.

I'm leaving this alone...let's sit back and watch what happens.

Um, being older than most on here ( I'd guess) and having a few miles under my belt ( Heck, I put 15,000 a year on my bike, and we have an actual winter here,) while driving about 45,000 miles/year, I'd like to point out that:

a.) I drove on cheap tires & recaps in my younger,poorer days
b.) I drive everything I own as fast as I can as often as I can (The Libby cuts fuel pressure at 107 MPH)
c.) I only inflated the 215/85r/16's on my 8,000# CTD dually to 65# when I was really loading it
d.) I have never had a blow out

What the heck is this guy and his family doing to have so many dern blowouts? Anyone knows that the depth of the tread left on a tire is a useless measurement for longevity. Is the tire 15 years old and left in the sun? Yep, but look at all of the purtee tread left!

Well it is purely subjective, I can just imagine what that Libby rides like.....


(EDIT: I ran into this gentleman in another thread. First, he is not a car guy and certainly not a Jeep guy. He is an eco-weinie with a touch of book learning. You will never tell him anything, just as this thread has shown. Common sense.........a rare commodity 3/11/08 )

_________________
LOST # 633
'05 KJ 3.7L/6spd/241 245/75/16 MT's
'88 MJ 4.0L/AW4/231 SWB HPD30 & trac-loc D44 w/3.73's
A dirty Jeep is a happy Jeep

[quote="ATXKJ"]I don't like the pig anecdote - sounds too much like your insulting people who disagree with you just because they disagree.
the may not have been the intent - but that's how it comes across.
Lighten up ...good Lord cant we joke around and have fun anymore? If I insult you , well you will know it for sure!

Yes 80 lbs would be fun to drive down the road in for sure. I was in the tire business for 11 years and this has to be the funniest but scariest thing I have heard!

Incommando I am with you ran my share of retreads, and run most of the time over the speed limit just cause I like that speed OH and the age thing.... I am at 50....uh.. plus so I know I have more miles under me than most on here

Oh well ...was going to use another one of my Grandfathers sayings but better not

Tom

_________________
MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

Tom being in the same age group as you (YES OLD FART) some times you run in to someone who knows sooooo! much more then we do. So what if we have socks and underware older then them. They had a thing on 60 Minutes about the new generation in business who never had to acheive they were raised with Mommy and Daddy calling teachers and such demanding they be given "A"'s instead of "C"'s because they need A's for college. So lets face it we have some one who is much smarter then us and know more then us because Mommy says so.

Sorry for the Hi-Jack but blatent stupidity should not be encoraged and as stated DANGEROUS the scariest thing is they will probably get one of our loved ones killed.
To Quote the Grand Father of Science Fiction Robert A. Heinlein "In a society where everyone carrys a Gun, You have a much more Polite Society" Think about it. Back to you normal broadcast.

_________________
LEAD FOLLOW OR GET OUT OF THE WAY
2002 Sport 4x4 3.7 L w/auto
Amsoil from bumper to bumper, Amsoil Air Filter
PIAA head light bulbs, Fog Light switched out to SilverStar 9005's
MagnaFlo Muffler, New Radiator, Rebuilt A/C system,Rebuilt Rear Diff, LBJ's twice
Dunlop 245/70-16 Rover AT

Well I am not as old as you to "old farts" but I do my share of driving ,50-80K a year just for work
I will say I agree 100% with the "old farts" on this one
including the stupid and dangerous part

I'll throw in my five cents. My 05 KJ sees a lot of trailering action. Usually in the 2500# range. I had the factory ST sneakers on it for 55k. The jeep was always squirrely at 70mph, especially in the hills of northern VT. Now, these ST's were run at 40 psi cold, from the day I picked up the jeep with 3 miles on the clock. I tired running them lower, but the sidewall flex really made increased the pucker-factor when towing. The tires have worn completey even from one side to the other, and had a decent size contact patch. I recently inherited my Dad's 02 Rene that he just put Dunlop Rover A/T. I put his tires on my KJ and then aired them up to 40 psi and had very little contact patch, and it rode like my old 3500 CTD when the butt-head tire guy aired up the new BFG A/T to 80 psi. So, I dropped the tire pressure until it had a decent load-bubble and good contact patch. That turned out to be 35 psi. When pulling the trailer through VT, there is almost no wind induced sway, and the ride is respectable. Crisp, but not harsh.

_________________
05 Liberty Rocky Mtn.
02 Renny...Traded for 2010 F150, 8200 GVWR, Plow prep, Max tow
1983 Husq. Model 61, modded
Husq 335 XPT, trail saw, modded