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I am from Holland so exuse me for mis-spellings and poor Englisch.

On the dutch camperforum the question of tire-pressure was asked often, but now not anymore.
I have got a copy of the first page of the European Tire&Rim Technical Organisation 2007 standard manual.
On that page some formula's witch the big tire-facturies use to calculate the correct tire pressure, for normal car tires on the road.
I have simpliefied them to 1 formula wich normal people can use.
Under the next link you can find the car version and ideas for re-calculating when you have tires with chanched specifications.
http://board.carstyling.net/showthread.php?t=67492
Sorry, it is in Dutch so someone has to translate. Luckily the formula stays the same.
So here it is so you can work with it .

A=B*(C/D)^1.25
A= the tire pressure you want to know
B= the maximum tire pressure,which you can find on the tire
C= The actual weight on the tire, the most discussable item.
D= the maximum load for the tire, also can be found on the tire in lbs, kg, or Load-Index( search in list on internet for the maxload then).
The minimum is 1,5 bar =??psi but I have seen in lists for car-tire pressure that 1,4 as minimum is also used.
And mind that there are 2 (somethimes 4) wheels on an ax .

To calculate what weight the tire can bear at a certain pressure you can use the next formula.
C=D*(A/B)^0,8
A= the actual pressure on the tire
B=same as above
C= The load the tire can bare at the actual pressure
D = same as above.
2^2 meens 2 square 2 = 4 on mathematical calculators, also that of windows calculator jou can find a button X^y.

Mayby there is someone on this forum with mathematical interest , who can work it out . You can send me a personal message for more information or place it under this topic. Mind that you have to build in a savety-factor. When you add 10% to the weight on the tire for calculating , the car stil rides comfortabel.

greatings from Peter

 

I have a 99 Dakota that originally came with the 235/75/15 tires. I replaced those rims with the latter model 16" wheels and now have 245/70/16s on the truck.

Im finding that there is not a "perfect" tire pressure. To me you have to look at the wear pattern to see if you are over/under inflated.

Right now at 35psi the outer edges of the tire are not touching the ground,which leads me to believe that they are over inflated. Realize that the tires are brand new, i just replaced/rebuilt just about the whole suspension and had it aligned.

So right now Im varying tire pressures front and rear to get an even contact on the pavement.

 

There is no "perfect" pressure. Every pressure brings with it a compromise. Lower pressures bring a softer ride, but can degrade handling and increase rolling resistance. Higher pressures bring a harsher ride, but can decrease rolling resistance.

The maximum tire pressure molded on the sidewall of the tire is not necessarily the best pressure. It's simply the most you're supposed to put in (cold). The ideal tire pressure is likely much lower than that. Dodge recommends 35 PSI for most of these vehicles. I wouldn't go much lower, and I probably personally wouldn't go much higher (like much over 40). Remember that while increased pressure does decrease your rolling resistance, it also decreases your contact patch, which means less rubber on the road.

There are always compromises. Try a few different tire pressures and see what you like the best. I typically run about 5 PSI higher in the front, just because the fronts carry more load, and it keeps the wear more even. I'm running 40 PSI front and 35 PSI rear, and that's with 32x11.50R15s on 15x7 wheels. The rear tires may still be a touch "overinflated" because the outer 1" or so of tread does not touch the pavement. But so far, they're wearing fine.

 

rear 275/50/17 - around 32-35psi

front 255/50/17 - around 37-40psi

 

I am running 50 fr and 46 rear with 265-75-16 10 ply LT tires and I have noticed a slight gain in mpg. Yes it is a little bumpier, but I got new shocks so its not that bad. We these tires wear out I will put P265-75-16's on as these are a little lighter than the LT tires.

 

35 psi has worked just fine in my experience. Decent ride and mileage. I think alot has to do with what tires you are running and how the truck is used. My Dak seldom sees heavy loads and is 2wd. I have the original type Goodyears on that it came with and they say max pressure is 35 psi. The first set went 35,000 miles, which is typical for Goodyears and the way I drive . They still had some good tread left and were wearing perfectly across the face, but 2 had to be plugged so I went ahead and put on a new set. If I were to carry a load though I'd bumpthe pressureup accordingly.

Word to the wise- If you ever see those carcasses left by blown tractor trailers tires, steer clear because those steel belts in them will definately puncture YOUR tires. [:@]

 

I have load range E BFG AT's and I keep the fronts around 45-50 and the rears 40-45. If it gets lower than 40 up front I don't like the way the truck handles.

 

Check and see what the tire says for max PSI, that way you can compared... I usally have 40, but when I want a bit more traction, winter ect... bring them down to 30 ish.

 

I believe that the tire pressure furnished on the door jam is the correct pressure, because it relates to the model of the car and its all up weight, as other cars with the same tires have different all up weights.

 

Wow, holy old thread dude. Let it rest in peace.