Warning! Low Tire!
If you see this TPMS icon illuminated, it means your vehicle has a low tire. STOP, and check the inflation pressure in your tires. This warning light will come on if tire pressure in any of your tires falls more than 25% below the recommended inflation pressure (refer to your owners manual, or the tire inflation decal in the glovebox, driver door pillar or gas tank filler cap lid for tire inflation pressure recommendations).
The TPMS warning light should come on for about one second when the ignition key is first turned on for a bulb check. It should then go out if all of the tires are properly inflated. If it does not go out, or it comes on while driving, you have a low tire.
Tire Inflation Pressure Monitor Systems (TPMS) are being used on more and more new vehicles. Low tires are potentially dangerous, especially if a vehicle is heavily loaded and traveling at highway speeds during hot weather. A low tire under these conditions is a blowout waiting to happen. The inflation pressure of the tires should be checked regularly, but many motorist do not check their tires. That is why Tire Pressure Monitor Systems are coming into use.
Tires are designed to operate within a certain pressure range. The recommended inflation pressure can usually be found in the vehicle owner's manual and on a decal that may be located in the glove box or door jam. The recommended inflation pressure is designed to give the best combination of ride comfort, load carrying capacity and rolling resistance.
NOTE: The maximum cold inflation pressure on the sidewall of a tire is NOT the recommended inflation pressure. It is a maximum limit for the tire only. The recommended inflation pressure for most passenger car tires is 32 to 34 psi (cold).
Increasing the tire inflation pressure reduces rolling resistance (which helps fuel economy). It also increases the load carrying capacity of the tire. But it also increases ride harshness. The maximum inflation pressure (which can be found on the sidewall of the tire) should never be exceeded because too much pressure may overstress the tire and increase the risk of tire failure.
Decreasing the inflation pressure improves ride quality by making the tire softer. Under certain circumstances this may help improve traction a bit. But lowering the pressure also reduces the tire's ability to carry weight and increases rolling resistance (which hurts fuel economy).
A low tire also wears faster. Why? Because increased rolling resistance and flexing in the tread scrubs away the tread. As the miles add up, so does the wear and eventually the tread is down to the wear bars. Once the wear bars are flush with the surface of the tread, the tire needs to be replaced.
The increased friction in the tread and the sidewall that results from underinflation also generates heat. All tires are engineered to operate within a certain temperature range, which you'll find on the side of the tire (A, B or C, with A being the best). When a tire is underinflated, it runs much hotter than normal. This may or may not create a potentially dangerous situation depending on how low the tire is, how fast the vehicle is driving, how heavily it is loaded and the ambient temperature. The lower tire, the more heavily loaded the vehicle, the faster is is traveling and the hotter the weather, the greater the risk of a blowout.
A blowout can have deadly consequences because it often causes the vehicle to lose control. If the blowout occurs on a vehicle like a truck or SUV with a high center of gravity, it greatly increases the risk of a rollover.
KEEPING AN EYE ON TIRE PRESSURE
Tire pressure needs to be checked regularly (every couple of weeks) because all tires lose pressure over. Where does the air go? It seeps out through microscopic pores in the tires, tiny leaks in the bead seal, and even through porosity leaks in alloy wheels. Some tires tend to seep more than others, and if a tire has a tiny puncture or a cut, it can lose a lot of air in a hurry.
You can't always judge a tire's inflation pressure by appearances alone. By the time a low profile radial tire appears to be low, it may be 10 to 15 psi underinflated.
According to a recent survey by the Car Care Council, 54 percent (that's over half!) of vehicles inspected during National Car Care Month were found to have improperly inflated tires. Most were low, but some were dangerously overinflated, too.
The Government Accounting Office estimates that probably 250 lives a year might be saved by reducing the number of fatal accidents that are attributed to underinflated tires.
The point here is that many motorists rarely check the inflation pressure in their tires, and if they do they may not do it correctly. Tire pressures must be checked when the tires are cold because driving generates friction and heat that increases the pressure inside the tires. The outside temperature also affects tire pressure (pressure drops about 1 PSI for every 10 degrees F).
Checking inflation pressure also requires an accurate tire guage. We've seen cheap tire gauges that are off as much as 6 psi right out of the package. The gauges on many gas station tire inflation machines are even less accurate.