air is everywhere should be free

Most people run tires at the pressure posted on the sidewall of the tire the problem with this is that the pressure is for max load of the tire and most cars dont even come close to maxing out that weight. The best thing to do is play with the pressure till it is where it should be. I have a jeep and run kuhmos the side wall says 35psi and max load of 2800lbs. if you take the weight of the jeep it is not even near the over 10k lbs that the tires can take at 35psi I run my tires at 28psi and it works good for me and have no adverse tire wear.

Just my .02 if I am wrong someone please let me know but this is what I was told by a friend who works for a tire shop

You're correct, Sabre.

Personally, I scale my vehicles front tires and rear tires to determine the exact weight on each, then inflate the tires accordingly.

If a vehicle is driven daily to work, with only one occupant, then the same vehicle is loaded up with the family and assorted gear on weekends, the tire pressures should be adjusted for the additional weight. But how many folks do that?

I've lost count of the times I've seen a van, loaded with people and the roof rack full of gear, running 75 to 80 mph on half bald, under inflated tires with the ambient temperatures in the 100+ degrees. Disaster looking for a place to happen. And when it does, they want to sue the tire manufacturer.
Go figure.

I think those folks are running nitrogen betwixt their ears.

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Pontificating Dogmatist

Of course this makes sense, but the next most logical question is: how much pressure, exactly? If I am a single occupant, driving a full size sedan with only myself in it 99% of the time, how much do I adjust the PSI downward? 2, 3, 6? PSI?

My point is that adjustment is highly subjective, and any attempt to come up with a number inevitably to a huge guess. So although I can see the logic in lowering my PSI, I have no sense of how to do that well, so I just leave it at the "recommended" tire pressure...

Tough guess....

Excellent points, World.
I suppose by trial and error. Watch the tread for wear patterns.
About the time it's figured out though, it's probably time to buy new tires. If so, buying the same brand and type would make sense, if they're still available.
Also, those infrared temperature devices can be used to take tire temperatures. Run four tires at different pressures and check the temps. But all that takes time and effort most aren't willing to expend. I'm a numbers cruncher by nature, so I find it interesting. Others might not.

All in all, I think there's a lot of forgiveness in tires these days, which is a credit to the tire manufactures. I think under inflation is more serious than over inflation.

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Pontificating Dogmatist

Curiously, I visited a Tire Kingdom here this evening and asked them if they have any throwaways (new tires at seriously discounted prices). They said we have a special on some very good tires called Kumho.

So if he can get the sizes I need, which are different on front and back of the car, then I'll take your suggestion. They seem to have a tread pattern which matches what I think I want, and they come at half the price of the Michelin PS2's I was thinking of putting on the car.

We'll see.

Kumhos are great tires! Used it for my Galant awhile a go, very good. Popular with the local autocross folks. Grippy, but slightly faster wearing than some the brand name ones. But goodyear's performance tires seem to wear out the fastest! Though they are often the grippiest.

Other than softness of the rubber, are there any other determinants of grippiness? Tread pattern, width of the tire...

Directional tires or the ones that have treads that look like arrows and can only be used on certain positions have better grip but much less tread life. I got Solus 16 grand touring Kuhmos. A little less high performance if you really want to push it to the limits, but 60,000 mile tread life. I have about 22,000 on them and they look like new. Check pressure about once every week and rotate at 5,000. They handle almost as good as the Goodyear Eagles and last about 2 to 3 times as long. Go to the Tire Rack and you can find all the info and lots of user feedback on any tire you can imagine.

If you want to know the proper inflation for a tire, for a given load, there are two methods we use on race cars, either works. First, find a local stock car racer in your neighborhood and ask if you can borrow his tire pyrometer. (He'll be the one with the garage lights burning 'till one or two in the morning, every night.) The second method is with a scribe, but you would have to wear a lot of tire off to get a reading with that. Works fine for race cars, cause we burn the rubber off 'em pretty quick, but not so practical for a street vehicle.

Run the vehicle down the road a few miles to get up to normal operating temperature, pull off in a safe area and stick the pyrometer in the tread at the center and about one inch in from each side and record your readings. Move quickly as they cool off pretty fast. If it's inflated properly, the three temps should be close to the same. If the center is considerably higher than inside and outside, you have too much pressure. Let a few pounds out and try it again. If the center is cold, it's underinflated, add a few pounds and try again. The outside edges of the front tires will most likely bit a little hotter than the insides due to toe in. This is normal on a street vehicle.

It takes a while, but this WILL tell you the proper inflation. Oh...and when you return the pyrometer, throw the guy a couple bucks. I can gaurantee he needs it.