Tire pressures

[railbuff]

My new 2500HD is equipped with the stock 245 Steeltex A/T tyres which I may trade in for 265 Michelin LTX M/S. Irrespective of this, my concern is the inflation pressure. According to the label on the drivers door, the rears should be at 80 psi and the front at 50 psi. I can only assume that these are the pressures when the truck is fully loaded.
The only time I am loaded is when towing our 5th wheel. The rest of the time there is no load in the truck apart from myself and wife. Under these conditions, there is very little tire footprint in contact with the road, particularly at the back. This could be dangerous when braking.
Where can I find information as to the correct pressures depending upon load carried?

[roegs]

You can see a Goodyear load / range chart by going here:

http://www.goodyear.com/truck/pdf/LoadInflationBook.pdf

Depening on the pin weight of your 5th wheel you still might not need the full 80 lbs in the rear.

[Captain Mal]

Railbuff,

About 135,000 miles on my truck. Probably close to 65,000 delivering large trailers. I always run 80psi in all 4 tires while towing. If it's a long return without a trailer, I drop to about 60 in all tires.

Right now my rear Steeltex's have about 56,000 miles on them and look pretty good. That is in marked contrast to other mileage reports I have read here.

This is what I do and this is what I get. Never have I felt there were any safety issues arising.

[Viking]

Railbuff, the figures given on the door satisfy the GVWR of 9200#. You have to experiment to find what is best for you. I run 60 front 55 rear when empty and 60 front 80 rear when loaded. I live 11.5km north of 401 on Shannonville Road. Not far from Picton via Marysville.

[LanceW]

I stole this idea from another member a while ago- take a carpenter's crayon and put a stripe across the treads of each tire. Drive truck. Look at the tires. If the stripe wears in the middle first, decrease your pressure. If the edges wear first, blow 'em up.

[ratlover]

I got this off an offroad forum that got it off a travel trailer forum......

"AccessMaster

The Real Answer to Tire Pressure
I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air pressue in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.
So how do I get a 2 Rivet rating? Does this long explanation help or hurt? "

Or supposedly if you weigh your truck and make a proportion outa it it will give you what to run. 80psi is for full weight so if you are at 1/2 the rated weight then fill her up to 1/2. I have never tried this since I find it a PITA to wiegh my truck but it is something I really need to do especially when I throw my plow up front.

[hoot]

ratlover,

Good post. Makes sense.

Since I don't load my tires with heavy weight, I found the higher pressures translate into a terrible ride, especially with these new Pro Comp 33/12.5-17's. I recently dropped my pressure from 45 to 40 and noticed a significant difference in ride quality. Not bad now.

[roegs]

Excellent post ratlover. Those folks that insist running with max air pressure (even too much when towing) must have good backs that enjoy a harsh ride! Its pretty easy to stop at a scale, find your weights, and adjust the air based on a load range table.