Tyre Pressure Monitor Systems (TPMS)

Tyre Pressure Monitoring Systems

Have you ever seen a vehicle with one or more tyres that appear noticeably low on tyre pressure? What if the vehicle with the low tyre pressures is the one you're driving? Wouldn't you want to be warned?

Maintaining the correct tyre pressure for a vehicle is an important factor in how much load its tyres can safely carry. The correct pressure will carry the weight without a problem. Too little tyre pressure will eventually cause catastrophic tyre failure.

Tyres are made of individual layers of fabric and steel encased in rubber. If a tyre is allowed to run low on air pressure, the rubber is forced to stretch beyond the elastic limits of the fabric and steel reinforcing cords. When this happens, the bond between the various materials can weaken. If this is allowed to continue, it will eventually break the bonds between the various materials and cause the tyre to fail. And even if the tyre doesn't fail immediately, once a tyre is weakened it won't heal after being reinflated to the proper pressure. So if a tyre has been allowed to run nearly flat for a period of time, the tyre should be replaced, not simply repaired or reinflated.

Studies have shown that running tyres with too little air pressure is not uncommon. It's been estimated that about one out of every four vehicles on the road is running on underinflated tyres. This also means that one out of every four drivers is needlessly sacrificing their vehicle's fuel economy and handling, and reducing their tyres' durability and tread life.

What types of systems are being used? How do they work? Which works best?

One option is to install a direct tyre pressure monitoring system that uses pressure sensors located in each wheel to directly measure the pressure in each tyre and warns drivers when the air pressure in any of their tyres drops at least 25% below the recommended cold tyre inflation pressure identified on the vehicle placard. Another option is to install an indirect tyre pressure monitoring system that would warn the driver when a single tyre has lost at least 25% of its inflation pressure compared to other tyres on the vehicle. While direct systems could offer more precise warning thresholds, indirect systems cannot offer the same information or accuracy.

Direct Monitoring Systems

Direct tyre pressure monitoring systems measure, identify and warn the driver of low pressure. Because direct systems have a sensor in each wheel, they generate accurate warnings and can alert the driver instantly if the pressure in any one tyre falls below a predetermined level due to rapid air loss caused by a puncture. In addition, direct tyre pressure monitoring systems can detect gradual air loss over time. Some direct systems use dashboard displays that provide the ability to check current tyre pressures from the driver's seat.

Direct systems attach a pressure sensor/transmitter to the vehicle's wheel inside the tyre's air chamber. Most Original Equipment and some aftermarket systems attach their air pressure sensor/transmitter to special tyre valves. While the presence of a metal clamp-in valve typically identifies the presence of a direct tyre pressure monitoring system, special snap-in rubber valves have also been used to support direct system sensors. The transmitter's signal is broadcast to the in-car receiver and the information is displayed to the driver.

Some aftermarket and Original Equipment direct monitoring systems attach the sensor/transmitter to the wheel with an adjustable metal strap. These sensors/transmitters and their straps only weigh a few ounces and allow virtually universal application on car wheels. Since standard snap-in rubber valves are still used for these applications, it is important that the owners of these systems let their us know that the vehicle is equipped with a direct system banded to the wheel before they change the tyres.

R-Tec works with aftermarket wheel manufacturers to develop wheels that can take thet tyre pressure monitoring sensors/transmitters. This results in our ability to offer a wider selection of aftermarket alloy wheel styles that accept Original Equipment direct system components. Additionally, the R-Tec’s fitment specialists have carefully determined which aftermarket wheels will be compatible with the vehicle and system installed for customers purchasing Tyre & Wheel Packages or wheel upgrades.

Indirect Monitoring Systems

In the interest of providing a lower cost Original Equipment system, indirect tyre pressure monitoring systems were developed by vehicle manufacturers wishing to comply with the law while minimizing development time and cost. Indirect systems use the vehicle's antilock braking system's wheel speed sensors to compare the rotational speed of one tyre to that in another position on the vehicle. If one tyre is low on pressure, its circumference changes enough to roll at a slightly different number of revolutions per mile than the other three tyres. Reading the same signal used to support ABS systems, the vehicle manufacturers have programmed another function into the vehicle's onboard computer to warn the driver when a single tyre is running at a reduced inflation pressure compared to the others.

Unfortunately, indirect tyre pressure monitoring systems have several shortcomings. Indirect systems won't tell the drivers which tyre is low on pressure, and won't warn the driver if all four tyres are losing pressure at the same rate (as occurs during the fall and winter months when ambient temperatures get colder). Additionally, our current experience with indirect systems indicates that they can generate frequent false warnings. We have found that false warnings may occur when the tyres spin on wet, icy and snow-covered roads. In these cases, the false alarms would train the driver to disregard the tyre pressure monitoring system's warnings, negating its purpose completely.

Aftermarket Tyre Pressure monitors (TPMS) are available to purchase and can be fitted into most aftermarket wheels. Please talk to an R-Tec sales adviser.