Air pressure in a tire depends on what?

Air pressure depends on the duty the tire is put under. On a normal passenger car a nominal pressure of 35psi cannot hurt anything. From grocery getter's to Mercedes Benz, believe me, it will work without fault. The door placard may say different, but it's the gospel in P metric 4 ply passenger tires. 6 ply tire should operate in the range from 40 to 50 psi. 8ply 50 to 65 psi. 10ply 65 to 80 psi. The higher of all said ranges being the max cold psi operating pressure. The more you pull or the more weight you haul, the closer you should be to the maximum pressure for optimal cooling of the tires. Otherwise you risk a low pressure blowout. Similar to those that run tires flat, not knowing, and blow them up on the roadside. These tires generate too much heat and cause the tire to fail catastrophically. Hope this helps. This comes from 15 years of seeing failures in the tire business.

I disagree. You should run the exact tire pressure listed in your owner's manual or on the driver's door post. That pressure will give you the very best handling, mileage, and ride. That pressure is what the engineers that designed the car have recommended. I believe they know way more about it than the above poster or me for that matter. Increasing the pressure will adversely effect the ride, & handling of the car. Stick with the recommended pressure and you cannot go wrong. Check the pressure when the tire is cold.

Okay so the moderator didn't care for my answer. He had an Excellent point. Here is mine in reply. Tell the families of the people that died in the Ford Explorer/Firestone rollovers that the engineers knew what they were talking about. They put 26psi on the door placards of the Ford Explorers that killed people. Most vehicles today are real close to 30psi. That might have been partially Firestones fault but if the door placard would have stated 35psi and followed, those people would be alive today. This incorrect low pressure created too low of a threshold for error. The manufactures of cars now adays are trying to find an amends between good ride and the over sized tires they are putting on cars now. These tires have no sidewall which is where a good riding car begins. In my personal opinion they are dropping air pressures to compensate for lesser quality suspensions for a better ride. There are too many variables for a default answer of go by the door placard. Hydroplaning, poor fuel mileage, premature tire wear, nonresponsive handling, and improper tire shoulder wear are all results of cars the reflect close to 30psi. Tires ran at 30psi even properly rotated will wear out premature in the shoulders. You will have almost 1/2 tread remaining in the center of the tire upon replacement. I'm not telling anyone to, but I run my car tires at 40psi cold all the time. I experience long and even wearing tire life, better fuel mileage, great water evacuation, responsive handling, and much more. So you consumers choose. Give all the rest of your money to the oil companies. In increased gasoline use and horrible tire wear. The base in tires is carbon black. Carbon black is achieved from crude oil. The engineers know a lot, yes. The dealership is a direct extension of the engineering dept., correct? Then why does no one with a brain buy tires at a dealership. Because there are very few stealerships, yes stealerships, that knows tires. 3 rules on buying tires. Don't buy from stealerships, clothing stores, (Walmart, Sears etc..) and last but not least........Buy from a tire dealer who knows tires. Who has common sense and who can look at your vehicle and give you recommendations that will save you lots of money in the long run. All my efforts are to benefit the consumer and keep money in their pocket.

Ok, I will answer your points one at a time and then the conservation will be over. You may have worked on installing tires but I built them. I know exactly how they are constructed.

1. You say you run 40 lbs on all your tires. That is on the average tire 5 lbs over the maximum allowed pressure the tire will hold. Running more pressure than the max is dangerous.

2. Tires inflated to the pressure recommended by the manufacture will NOT wear out on the shoulder if they are kept at the proper pressure. They wear on the shoulder due to under inflation which you know as well as I you see all the time. People do not check the pressure and keep the tires inflated properly. I keep my tires inflated to the manufactures recommended pressure and have never had a tire wear on the shoulder. It simply will not happen if you keep them inflated properly.

3. The Ford Explorer case was a rarity in the first place. Did the tires blowout due to low air pressure or did they blow out due to overloading of the vehicle and or low tire pressure way below the recommended 26 lbs pressure. To say the putting 26 lbs of pressure in the tires caused the blowout and deaths of people is ridiculous. Were the tires defective in the first place? Or was the problem a combination of under inflated tires way below 26 psi, overloaded vehicles, defective tires, and driver's panicking when the tire went down. I do not know the answer to these questions and neither do you.

4. So in essence you are recommending that all consumers ignore the recommendation of the people who designed the car, the suspension, and chose the size tires to install. Spent countless hours testing these combinations and then came up with the best tire pressure for handling, ride, and mileage. They should not believe these engineers and take your advice. If people want to take your advice then that is their choice.

I still recommend airing your tires up to the recommended pressure listed in your owner's manual and on the driver's door post. That it my advice and the advice of almost any expert you care to read.

You gave your advice and I have given mine, so this question is now closed to any more discussion.