tire pressure?

http://www.automedia.com/Optimizing_Tire_Pressure/ccr20010801tp/1



You'll need a piece of chalk, a tire gauge, a pen and a note pad. Make a chalk mark across the tread as pictured, on one front and one rear tire, and then drive a quarter mile or so in a straight line. Stop and study the chalk marks and note the pressure readings on the gauge.
This tire shows over-inflation, having relatively intact marks at the shoulders while the center of the line is more worn. Ideally, the chalk would have faded evenly across the tread surface. Let out some air and try again.

One simple method for finding the right pressure for your vehicle is to draw a chalk line across the tread, then drive a bit and check the line. Even wear is good, while the line fading in the center indicates over-inflation. Worst is when the chalk mark wears off at the outer edges (shoulders) first, meaning that the pressure is too low. Under-inflation lessens the tire's load capacity, can make for squirrelly handling and, most importantly, makes the tire run hotter. Hot tires tend to disintegrate, regardless of who made them. Consequently, it's better to err on the high side, even if ride quality may suffer and the tire wear pattern could be less than optimal. However, do not exceed the maximum pressure as stated on the sidewall—there can indeed be too much of a good thing.


Once the lines wear off evenly, note those pressures for future reference. While the inflation must be identical for both ends of an axle, the front tires will often require a slightly higher pressure since they usually carry more of the weight of an unladen vehicle (most engines are up front).


Gauging Pressure
It doesn't really matter how accurate your tire gauge is as long as it's consistent and you use that same one every time. Also important for repeatability is to measure the tires either cold or warm, then stick with that measurement method since tire pressure vary quite a bit with temperature. Last, but not the least, if adding load to the vehicle, don't forget to add to the tire pressures accordingly.

 

The chaulk method should be done for every set of tires. Tire pressure for the vehicle will vary between makes of tires, and manufactuers.