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Kate on Cars - Sep 2013 - Blowouts and Tire Pressure Monitors


Kate on Cars - Sep 2013
Blowouts and Tire Pressure Monitors
the Basics You Want to Know

by Kate Jonasse

Tire blowouts are no fun, unless you enjoy practicing your defensive driving skills. A blowout is when a tire bursts – this can happen if an object strikes the tire, if the tire has a weak spot, or if tires are underinflated. Low tire pressures are a major cause of tire blowouts. When tires are underinflated, the sidewalls of the tire flex too much and overheat, which leads to the rubber losing its bond to the internal fabric and steel cord reinforcement layers, which weakens the tire and causes it to burst. Blowouts are a common cause of motor vehicle accidents.

As part of the TREAD Act in 2000, our National Highway Traffic Safety Administration (NHTSA) decided to make tire pressure monitoring mandatory on new vehicles as of 2008. These systems warn the driver if any tire falls more than 25% below the manufacturer recommended tire pressure. Early tire pressure systems came out a few years after the Act was enacted, and all model-year 2008 and newer passenger vehicles are equipped with a direct tire pressure monitor system (TPMS). Tire pressure monitors save many lives each year (assuming the driver corrects the pressure and doesn’t just ignore the light, of course).

Early TPMS

Early TPMS were indirect systems. Rather than measure tire pressures directly, they guessed at it by reading wheel speeds from the existing wheel speed sensors used by the ABS system. This was sort of a quick and dirty TPMS that used pretty much the components that were already on the vehicle, so it wasn’t very expensive to create.

The indirect systems would monitor wheel speeds at all four wheels. When a tire is underinflated, the tire diameter decreases thus the wheel spins a little faster than the other wheels while driving. The control module would notice the difference in speed, assume it was due to an underinflated tire, and turn on the tire pressure warning light in the instrument cluster to alert the driver.

This system wasn’t good enough to meet TREAD standards, because if all tires were underinflated but at similar pressures, the system would not warn the driver.

Current TPMS

Direct TPMS is more precise than the indirect systems, and it is on all 2008 and newer passenger cars. This type of TPMS uses a sensor in each wheel that sends pressure and temperature readings to the TPMS Control Unit. These systems are either high-line or low-line.

The main difference between high- and low-line direct TPMS is that high-line tells the driver exactly which tire is low, while low-line just gives a general warning that one or more tires are low. Both systems have a sensor and transmitter in each wheel. High-line also has an antenna at each wheel to pick up the location of the low tire, while low-line typically only has one central antenna communicating with all 4 sensors. The antennas transmit sensor signal to the control module for processing. If the module finds that a tire is underinflated by 25% or more, it will turn on a light or display in the instrument cluster.

In Case of a BlowOut

I hope you never have a tire blowout. But in case you do, know that many drivers’ first reaction to the noise and to the vehicle pulling (to the side of the blown tire) is to jerk the steering wheel back into place and hit the brakes. This is not what you should do. The recommended thing to do is to accelerate slowly or at least keep the vehicle speed steady – this helps the tires keep a good grip on the road. Then carefully guide the steering wheel to gain control of the vehicle – jerking it can cause you to lose control of the vehicle. Then gently and calmly pull over to the side of the road while slowly decelerating, keeping control of the vehicle and of your mind. Stay calm. It will be ok.

Tires are a very important safety item on your vehicle. Ask your tech about their condition at each service, and replace them promptly when they are worn. Let me know if you’d like a free lesson on how and where to get your tires aired up. Remember – prevention is cheaper and safer than having to clean up after the fact. Drive safe.