FastJake

In case you missed it, advising other people when they come here for help is the entire point of this forum.

A door placard isn't going to have seven paragraphs detailing exactly what to do under various conditions, when using snow tires, carrying heavy loads, etc. Advising people to follow the manufacturers recommended pressure when carrying a heavy load, for example, is actually bad advice because the tires will get hotter and wear out faster. Worst case, they will blow out.

Blindly follow every manufacturer recommendation if you want, just don't criticize others for being smarter and going after better results.

Coal Buster

I worked in automobile safety for 5 years. You wouldn't believe how close to the edge some of these cars are built. FWIW, Toyotas always tested the best as far as going beyond minimum safety standards.

The best advise as far as carrying heavy loads is to use a vehicle designed to carry heavy loads.

FastJake

And what do you know specifically about tire pressure in cars? Because I haven't heard anything worthwhile so far. What have I been doing wrong all these years? And how have I not lost control and crashed running my Subaru's winter tires at 40 PSI instead of 30?

Coal Buster

Going over pressure will raise the center of gravity of your vehicle. Probably not a big deal with a Subaru, but that was an issue with Jeep Wranglers from a while back. I've been out of the game a while. The biggest culprit as i recall was the Ford Exploder. The only way to pass the rollover test was to set the fill pressure to a ridiculously low ~20psi, iirc. Ford then equipped the auto with tires that ran a minimum pressure of around 30psi. Under inflating led to dangerous overheating of the tire. Proper inflation of the tire led to increased rollover risk.

ThermionicScott 

That particular Ford Explorer deserves its own category for engineering/design facepalms. What is the user supposed to do when the vehicle can't perform safely as spec'd?

1saxman

I don't know why we lapsed in auto considerations, but following the door sticker and checking when the tires are stone cold can never be bad. In particular, you never want to let the cold pressure slip to more than 2 psi below the recommendation. Certain vehicles have certain recommended pressures for safety concerns such as with the late Saturn VUE, which experienced bead/rim separation under certain conditions and resulting loss of tire pressure, resulting in loss of control. The recommended tire pressure went from 30 to 35 and new door stickers were installed. If you raise the recommended pressure, you most likely will be letting yourself in for more road noise and less ride comfort, as well as possibly increasing wear to other suspension/steering components.

As for the bicycle, I'm surprised no one mentioned (unless I missed it) that rims have maximum pressure allowances too. This is because tire pressure exerts spreading force on the rim, which becomes more critical as the rim wears from brake application. Many rims have failed in this way. Just another factor to keep in mind when considering higher pressure.

FastJake

Which is why I said, "Rollover has little to do with it except in a tall top-heavy SUV. I guarantee you won't get a Corvette to roll over if you inflate all the tires to 10 PSI or 60 PSI (though you will certainly have other serious issues.)"

Of course a Jeep Wrangler is going to roll over if you push it too fast into a corner. The solution isn't to run the tires at a dangerously low pressure, it's to not drive it like a sports car.

Your Ford Exploder reference is a perfect example of this. Everyone probably remembers the Exploder/Firestone tire disaster. The problem was a combination of Ford speccing an unusually low tire pressure (26 PSI if I remember...) and the Firestone tires being slightly more prone to blow-outs from heat. If an owner forgot to check the pressure and it dropped to the low 20s the tires would heat up too much on the highway and blow out. This causes the vehicle to pull violently to one side and the Untrained Driver's natural reaction is to jerk the wheel in the opposite direction to compensate. This will cause a roll-over every time. (The correct procedure is to slow the vehicle down gently and try and maintain a mostly straight path.)

Bottom line, those vehicles were unsafe during certain maneuvers no matter what you did. There was no winning. Except maybe for Ford (and others) that raked in hundreds of millions on the ridiculous SUV craze.

rydabent

I guess I dont understand people that refuse to believe what the manufacture suggests, and have engineered the specs of what the pressure should be. A minimum is suggested to prevent snake bite flats. The maximum is set to the engineered strength of the tire. Seems pretty simple to me. Why claim or argue you know better than the people that built the tire????

ThermionicScott 

The people that built the tire don't know how much I weigh, how I ride, or what roads I'll be on. You tell me how 110-120 psi (as my 700x25C Continentals were marked) is simultaneously the ideal pressure for a 90 lb waif and a 350 lb uber-clyde!

FastJake

For better performance. I have some 29x2.1 tires that give the typical range of 40-65 PSI. If I rode them at 40 PSI on mountain bike trails my back would explode from the impacts. I run them at less than 20 PSI and I've never dented a rim or pinch flatted. But I only weigh 140 lbs.

Manufacturers can't take every possible scenario into consideration. These numbers are guidelines to be used as a starting point and fudged as necessary.