Tire pressures are listed on the sticker on the back of the driver's door opening.
The variable you're concerned with is the weight of the vehicle that has to be supported. The pressure is so many pounds "per square inch". That won't change unless the volume of the tire changes.
There's two things to keep in mind too about pressures. Most of the time manufacturers are going to specify a pressure that's on the low end of the acceptable range because that allows the sidewalls to flex more and provide a smoother ride. Higher pressures decrease rolling resistance so you'll get better fuel mileage, but some people take that to extremes. They incorrectly think if more is good, much more is better.
I'm a suspension and alignment specialist, but I got out of the business before the government-mandated tire pressure monitoring systems came along. Up to that point, manufacturers also had to consider which replacement tires you might buy in a few years. Most tires on new cars called for a maximum of 44 psi, but for decades there were tires rated at 35 psi maximum, and those are still available. I found that I had absolutely no complaints of ride quality when I set tires that called for 35 psi max to 35 psi, and tires that called for 44 psi max to 40 psi. Those are the numbers on the sidewalls, not on the door stickers. Most of those cars called for 32 psi on the stickers, so I was inflating the tires to more than the manufacturer wanted for ride quality, but not more than the tires were designed for. In my ten years at the dealership, I never looked at the stickers on the cars.
The tires that called for a maximum of 44 psi had softer sidewalls, so more air pressure was needed to hold the vehicles up and to withstand road impacts. Those are the tires that usually came new on those vehicles. The problem was what if the set of new tires you bought were rated at 35 psi max? You can't have "40 psi" on the door sticker when there's 35 psi tires available because most people who DO bother to check their tires will forget and they'll go by the door sticker. A 35 psi tire set to 40 psi would obviously be over-inflated, and when the pressure goes up even more when they get warmed up, the risk of a blowout increases a lot.
The engineers at Ford have seriously messed up alignment angles, and even made them not adjustable so we couldn't correct them, in a stupid attempt to provide real nice ride quality compared to their competitors' cars so they could sell more of them. In the case of the 1980's Escort disasters, front tires lasted 15,000 miles if you were lucky, but there was no way to know that before you bought the car, and the salespeople sure weren't going to tell you that. On the Explorer is where they lowered the tire pressure so much that the excessive sidewall flexing generated so much heat that the plies separated leading to blowouts. In the typical over-reaction by politicians who don't know anything about cars, they demanded new ones have tire pressure monitoring systems, but there's no standardization of how they work or the parts that are used, and the funny thing is, unlike air bag systems that they also have their hands in, tire pressure monitoring systems don't have to work, meaning you don't have to have the system fixed if it fails, and you can disable it without legal repercussions. They only have to be installed by the manufacturer, and of course you're required to pay for it.
The Explorers were fairly heavy vehicles but the specified tire pressures weren't sufficient, and you remember all the news stories about tire failures and people getting hurt. It was the brand of tire that came on those vehicles when they were new that made all the news stories, but what they didn't tell you was the same thing was happening with other brands of tires on those vehicles. All the problems disappeared when they made the tire pressure recommendation higher, and closer to the maximum rating.
Again, while most of my counterparts and I prefer more pressure than what's specified, common sense must be used. There's a limit to a good thing. No one will fault you for going according to the door sticker, regardless of the type of tires you have.
Thursday, September 25th, 2014 AT 9:05 PM