The tire manufacturer (of an aftermarket tire) has no idea whatyour vehicle weight is, so you will not be able to use a pressure specified by the tire manufacturer as a guidline. The pressure on the side of the tire is a maximum safe pressure - kinda like the max pressure on a spray paint pressure pot. This is the pressure you should never exceed, not the recommended daily driving pressure. There is a big difference.

Rich,

I guess the guy who made the video withdrew it from that site. Yes, the C4 guy (whom I know) was heading up a mountain road when he spun out. Luckily, neither he nor his car was hurt. He quickly realized that he had overpressurized his tires to 34 psi instead of the 30 psi to which he normally pressurizes them. Just 4 psi made his tires' contact area a bit smaller and hence, less "grippy".

Dave

 

Well I figured I was wrong but wouldn't the auto manufacturers pressure recomendation only work with the recommended tires? what if you replace your tires with tires of a harder or softer compound? I guess you would have to do your own testing huh? I never really paid much attention to the sicence of tires and tire pressure just always put 28 to 32 lbs and just replaced them when they wore out. some lasted longer than others but I just figured it to be the affects of driving habbits. the front tires on my '87 coupe are perfect and have little wearbut the rear are about done, slightly more in the center than the out sides. they are at 32 all around. Coopers. lots of good stuff in this thread too.

 

That all sounds right on to me Blueshark.
At the track tire pressure is crytical, and you can win or lose races with not the right amount.

I can remember just a few years ago now, Firestone, and all the problems people were having with their tires blowing out. People were getting killed because of the accidents. And they were warning people to use the correct pressure in there tires, and not under inflate them.

 

I run 34-36 in front and 36-38 in the rear of my Porsche (both within the factory recommended range, but on the high end) and it works well. It get only 20K miles per tire, but they wear very evently and that is par for the course for really extreme high performance tires.

On my vette, the original tires wore on the edges mostly at factory pressures, so I increased the pressure. Now, with oversize on all corners I have to guess, but I do an "ink pad" test on the tires until they seem properly inflated. But about 36 in front (275s) and 28 in the rear (345 drag radials) seems to result in good handling and even wear.

It could be that run-flats need less air pressure than normal tires: with the tough sidewalls for run I would expect that. Still, if you replace the tires with the same model and inflat them the same way, you probably will get the same result.

 

That was a good site never the less.
Quite a few interesting videos there.