BATMAN

Sure you may be a safe driver, buckling up before you head out, adjusting your mirrors and keeping a close eye on the speedometer. But how often do you check your tires? The problem isn't so much defects, but just plain old maintenance.

A survey last year by the National Highway Traffic Safety Administration reported that 27 percent of cars and 32 percent of vans, pickups and sport utility vehicles had at least one tire that was underinflated. Eight percent of light trucks and 3 percent of cars had all four tires underinflated..

The survey estimates low tire pressure kills as many as 79 people a year with as many as 10,635 people a year injured. Underinflated tires also can wear out more quickly and reduce fuel efficiency.

In many of the accidents involving Firestone tires, they were not inflated to the pressure recommended by the manufacturer. Firestone tire failures have been blamed in 203 deaths and more than 700 injuries.

The survey considered a tire underinflated if it was eight pounds per square inch or more below the vehicle manufacturer's recommended inflation pressure. That's 25 percent for a common recommended inflation pressure of 32 psi.

Data collectors stationed at gas stations around the country measured the inflation pressure of 11,530 tires during two weeks in February.

"People need to make it a regular part of their maintenance, not only to check the oil and the other fluids in the vehicle, but checking the tire pressure," said NHTSA spokesman Rae Tyson.

However, those that do check the tire pressure make a common mistake, according to the NHTSA. Most people use a gauge, but then make a mistake: they read the side of the tire for the psi -- pressure per square inch -- and then inflate. It's confusing, because what you're supposed to do is look inside the driver's door for the correct pressure for your cars tires.

Width & aspect ratio
The "P" in front of the number stands for "passenger."* "215" represents the width of the tire in millimeters. "65" is the ratio of height to width. The "R" stands for "radial" and the "15" is the diameter of the wheel in inches. A "B" in place of the "R" means the tire is belted bias construction. A "D" in place of the "R" means diagonal bias construction.

*This tire example is based on the P-metric sizing system, a scale introduced in 1976 for compact cars. An older tire measuring system, the alpha-numeric, uses letters A through N to identify tire size and load carrying capacities.

Service Description:
"89H" in this example, consists of the load index (89) and speed symbol (H). This only appears on speed-rated tires.

DOT code:
The letters "DOT" certify compliance with all applicable safety standards established by the Department of Transportation (DOT). Adjacent to this is a tire identification or serial number. This serial number is a code with up to 11 digits that are a combination of numbers and letters.

Ply composition:
The sidewall also shows the type of cord and number of plies in the sidewall and under the tread. The DOT requires tire manufacturers to grade passenger car tires based on three performance factors: treadwear, traction and temperature resistance.

Load limit:
The maximum load is shown in lbs. (pounds) and in kg (kilograms), and maximum pressure in psi (pounds per square inch) and in kPa (kilopascals). Kilograms and kilopascals are metric units of measurement.

Treadwear, traction & temp.:
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test course under specified test conditions as one graded 100. Traction grades, from highest to lowest, are A, B and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The temperature grades, from highest to lowest, are A, B and C. These represent the tire's resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel.

To make it easier, some car manufacturers now offer automatic tire pressure monitoring systems. It's standard on new Corvettes with an onboard computer that checks the pressure in each tire, even when your driving down the road. The federal government hopes by 2003 to make air pressure monitoring systems mandatory on all new cars.

The Rubber Manufacturers Association has launched a multimillion-dollar campaign to encourage proper tire care called "Be Tire Smart - Play your PART." PART stands for pressure, alignment, rotation and tread, the key aspects of tire maintenance.

Only 4 percent of respondents to a survey conducted for the association last year mentioned tire pressure checks when asked what routine tire maintenance is done on their vehicles.

Fifty-five percent did not know where to find the correct pressure recommendation for their tires, which is in the owner's manual and on the vehicle doorjamb.