xp8103

I have a set of load-range "E" Michelin LTXs on my truck. I know that the max pressure is 80 pounds but what should the nominal, unloaded pressure be? For instance, I run the tires on my wife's car at 32 pounds where their max is 40 or something like that. Should I be running somewhere in the 70-75 pound range under normal conditions?

Shovelhead

I run 65 psi in the fronts on my Dually and 55 in the rears.
('cuz there's 4 of 'em)

chasd60

I run 55 front and 55 rear when unloaded........ but I too am still learning.

xp8103

So its sounding like 65-68 is a reasonable pressure then.

xp8103

Chas,
I wonder if 55 is a little low on our trucks? BTW, how'd the 2WD do in the storm last weekend?

TTHA33

Running under 50 psi on an "E" rated tire will damage it. It will cause the tire to chop and possible belt seperation. This comes from experience. I ruined a perfectly good set of Michelins this way. Now I always run at least 60 pounds empty and run them up to 70 when loaded.

Eskimo

80 front, 50 rear unloaded for me... I've got a heavy front bumper though.

Tmc243

The more air you run in your tires the more weight they will carry, the better your fuel mileage will be, the better the vehicle will handle (hi-way), the longer the tires will last, and the safer they will be at high speeds, BUT the more air you run the harder the truck will ride. So its got to be a trade off. You need to consider the way you drive. I hear on TV sometimes about "high speed persuits" with speeds of 80-90 mph, where I live (Houston) we call that rush hour. I normally keep my tires 75lbs. front 70lbs. rear, I will run the rears up to 75lbs. if I'm traveling or going to tow anything. I'm running the 265's instead of the OE 245's so I can leave my pressures a little below max and still be safe.

Shovelhead

If you run at Max Pressure while unloaded, you'll wear the centers faster as the tire will actually be overinflated.
You might see slightly increased fuel milage but at the cost of quicker tire wear.
Your wet traction could also be reduced due to decreased contact patch.

JMHO

latitud_rt

That's not entirely true. Running tires severly underinflated can cause damage but 50 PSI is not severly underinflated. Overinflation will cause rapid wear and poor traction in rain or snow. Anywhere between 50 - 60 rear and 60 - 70 front , unloaded should be fine. By the way, "E" rated is more about load carrying capacity not inflation. I used to have a Toyota Tacoma that had 31x10.50R15LT from the factory that according to Toyota they were supposed to be run at 26 front, 28 rear.

Check your door placard.

RAM2940

I have the michelin LTX's also. When i first got the truck i started out at 55 psi and drove a few thousand miles, realized they were to soft and bumped up to 60. Then upto 65 and finally settled on 70 psi on the front. Seems to have a decent ride and even tread wear. Also the sticker inside the door says 70 psi front. Rear tire inflation is more up to the load thats on the rear. I run run between 60 and 65 but it is a little harsh in the rear when empty.

Tmc243

Shovelhead,
With all due respect, with a radial tire the overinflation/underinflation relation to tire wear isn't near the what it once was with bias ply tires. The biggest thing that causes problems with tires is heat, the lower the inflation the more heat you tires will have at a given speed. As long as your not over heating your tires you should be fine. I copied some information off the internet that might help someone make a decision. The last paragraph comes directly out of a Chrysler shop manual (for a 99 3500). Note that Chrysler recommends max air pressure if you drive at speed over 75mph. I do, and this is why I keep my tire pressure up. I grew up in Northern Va. with all the curves and hills I don't ever remember wearing out the middle of a tire before I could wear out the outter edges.

A load range E tire is only a load range E tire if it is inflated to the correct pressure for the load. And that is critical also. Truck tires typically are inflated to carry the present load and this can vary day to day in commercial operations by knowledgeable people.
A 10-degree drop in air temperature will reduce tire pressure by 1 psi. The difference between summer and winter tire pressures can be as much as 8 psi, causing a fuel penalty..."
- Sikorsky
"How to get more MPG in the 90's"
For truck tires, a 10 psi drop in tire pressure will increase tire rolling resistance by 2%.
- Goodyear Tire & Rubber
Under-inflation is not only the tire's enemy for durability but is a significant contributor to increased rolling resistance and loss of fuel economy.
- Goodyear Tire & Rubber
Tires under-inflated by 15% will cause fuel penalties of around 2.5%, and a 30% under-inflation will increase fuel consumption by 5%.
- Goodyear Tire & Rubber
Maintaining tire inflation pressure is the most important tire maintenance function. Cost per mile benefits will directly result from good tire pressure control.
- Goodyear Tire & Rubber
Running tires at 20% under-inflation can reduce tire life by up to 50%.
- Goodyear & Michelin
Under-inflation will cause increased tire running temperatures and...leads to premature removal of the tire.
- Goodyear Tire & Rubber
Tire under-inflation will reduce tire life as follows: 20% pressure reduction causes a 25% tire life reduction, and corresponding figures for 30% under-inflation are a 55% tire life penalty.
- Schrader-Bridgeport
The National Highway Transportation Safety Administration estimates that nearly half of all passenger cars on the road have at least one tire under-inflated by 20 percent. That means, if the vehicle placard indicates the correct pressure is 32 psi (pounds per square inch of pressure) a 20 percent reduction would drop the pressure to about 26 psi.

"That seemingly small difference can mean the margin between control and out of control for the average driver," said Mac Demere, test driver at the proving grounds, "especially on wet road conditions."

To demonstrate that point and others, Michelin set up three test courses for the SCDOT trainers and executives. The first test was timed and required drivers to safely navigate a mini grand prix course as quickly as possible on wet pavement. First, the test was run with tires at correct inflation pressure. Then it was run with tire inflation pressures set 20 percent below the vehicle manufacturer's recommendation.
"With correct pressures, the tires are in contact with the road and evacuate water through the tread grooves to give the driver the best traction and performance," said Demere. "But when you lower the pressure by 20 percent, the center of the tread no longer makes contact with the road. Basically, your tires are riding on water, making it more difficult to keep the car under control."

-MICHELIN

Proper tire inflation would save 25,000 lives each year.

TIRE PRESSURE FOR HIGH SPEED OPERATION
Chrysler Corporation advocates driving at safe speeds within posted speed limits. Where speed limits allow the vehicle to be driven at high speeds, correct tire inflation pressure is very important. For speeds up to and including 120 km/h (75 mph), tires must be inflated to the pressures shown on the tire placard. For continuous speeds in excess of 120 km/h (75 mph), tires must be inflated to the maximum pressure specified on the tire sidewall.
Vehicles loaded to the maximum capacity should not be driven at continuous speeds above 75 mph (120 km/h)
For emergency vehicles that are driven at speeds over 90 mph (144 km/h), special high speed tires must be used. Consult tire manufacturer for correct inflation pressure recommendations.

Sorry to but please if your are going to error on tires pressure do it on the high side for safety.

Shovelhead

A picture is worth a thousand words.

My rear tires after running @ 70 PSI for a year.

These are 235-85-16 Cooper SRM II Load Range E Steel Belted Radial tires.
Notice the increased wear through the center portion of the tread.
The siping is gone.

Now running @ 55 PSI.

Mopar1973man

Shovelhead,

I see you just about ate the center out of the tire... Sorry...

I've been trying different pressure to load on my tire and found this to work...

Normal weight
50 PSI - FRONT
40 PSI - REAR

Heavy Hauling - Firewood
70 PSI - FRONT
60 PSI -REAR

Notice the tire pressure jump a even +20 PSI front to rear... Being that the total truck weight jumps too! Best way I found is to weight your truck and figure out you pressure to weight.

So far I've got 46,000 miles on a set of BIG O XT - 265/75R16 tires... right at 1/16 difference of inch from the side to the middle of the tread.

My truck hits the scales right around 7,800 - 7,900 lbs. Hmmm... I guess I got some thing right when my MPG's are at 20 - 21 MPG... Hmmm...

Also rotate you tires often... I check the tire pressure once a week...This all helps!

Shovelhead

With the pressures dropped, they seem to be at least wearing evenly now.
Still should be OK until late Fall.
Us Guys with "Training Wheels" operate under different parameters from you "Under-Tired" folks.