Optimizing Tire Pressure
Proper inflation puts the most rubber on the road
Jimmy Nylund / autoMedia.com
About the only positive result from the current Ford/Firestone situation is that more people are now aware that proper tire inflation pressures can be crucial. Luckily, running the correct pressure is relatively easy—but how do you know what it is? That depends on a number of factors, including vehicle weight, tire specs, air temperature and even personal preference. Newer vehicles have the manufacturer's recommended pressures on a decal in the door jam or glovebox, but those numbers are for a stock vehicle with a full load.
Air Apparent Running the correct pressure is relatively easy—but how do you know what it is?
Tires lose pressure over time, so checking the inflation at least every couple of weeks is important. While you have your tire gauge out, you might as well set them at a correct pressure for your vehicle/tire/load combination.
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).
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.
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. http://www.automedia.com/Article/ima...0801tp_s02.jpg
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.