The next time you go out to your car take a few moments to kneel down and read your tires. The latest ones on the market have something new to tell you.

In the past, a scan of the sidewall gave you the tire's brand name, size and recommended inflation. But that short story is growing into a novel. Now you can read how well your tire measured on three federally required tests of treadwear, traction and temperature resistance.

For treadwear, the tire will bear a number that could range from 60 (by 10s) to 220. Generally, the higher the number, says the Transportation Department's National Traffic Safety Administration, the longer wear you should expect to get from the tire.

That means, say the experts, if you find two tires of the same size selling for $50, and one rates 100 and the other 200, you'll get twice the wear for your money with the 200.

Traction and temperature resistance are rated "A," "B" or "C." Tires rated "A" for traction, they say, should "stop on a wet road in a shorter distance."

"A" for temperature "means the tire will run cooler . . . and is less likely to fail if driven over long distances at highway speeds."

All automobile tires manufactured since last Oct. 1 are required to bear that information, with the exception of snow tires and the small-size spares. This Tire Grading System, says the traffic safety administration, was developed "to help you select a safe and economical tire."

But not without some squealing from most of the country's tiremakers, who fought the legislation and, says Thomas Cole of the Rubber Manufacturers Association, consider the treadwear labeling information "misleading." Uniroyal, however, has praised the system as a "progressive, efficient way to buy tires."

Support for the grading system also comes from the American Automobile Association. Automotive engineer Catherine Van Sant says, "We're pleased with the grading system. It is something that was needed in the market place. It's a good relative measure." More than 2,000 different brands, kinds and sizes of tires are tested.

One problem, she says, is not enough tire buyers know about the new labeling yet. A spot check of two big tire dealers in the Washington area supported her statement. One could remember no customers asking about the grading system in the past few weeks, and the other said only a dozen had brought it up.

Prior to the grading system, says Clarence Ditlow of the non-profit Center for Auto Safety, there was "absolute consumer confusion about buying tires. While it's not perfect, it's a big help."

Cecil Brenner of the federal Office of Automotive Ratings, who helped develop the program, thinks it's still "too soon to tell how well it is working." He is quick to point out the ratings a tire earns are only relative, but they do give the customer a basis for comparison shopping.

A tire rated 100 in the official treadwear test, he says, would be expected to last 30,000 miles. For each additional 10 points, the projected life under test conditions would be 3,000 miles more. But actual tread life will depend on where and how you drive and whether your tires are properly inflated. d

In Utah, the same tire may only get 14,000 miles, he says, because the lava-type rock used in road construction there chews up rubber faster. In this area, where softer limestone is used in paving, the tire may get 19,000 to 20,000 miles. Mountainous driving also causes faster tire wear, according to a Uniroyal study.

The treadwear tests are conducted on several hundred miles of roads around San Angelo, Texas. In most cases, the tire companies do their own testing to federal standards or hire a private company to do it for them. The government, says Brenner, makes spot checks on their accuracy.

Bias tires, he says, tend to rate from 60 to 120; belted bias from 70 to 210 and radials from 120 to 220. No tire rates a "C" for traction. About 50 percent of the tires now sold are radials.

To buy the best type of tire for your driving needs, the traffic safety administration suggests:

If you drive often on wet roads, pick a tire with high traction grades.

For high-speed driving, shop for one with high temperature resistance.

Pick radials for long-distance highway driving because they "will give you the most tread life."

If you are a city driver, consider skipping radials. In the city, where you may be scraping into curbs, they "are more sensitive to sidewall damage."