Automobile maintenance is important. Period. However, in the rush of your daily life, you may forget about the well-being of your car's tyres. You won't just hurt the tyres but also put lives at risk if the tyres have pressure lower than necessary. One way to ensure that the tyres have the right pressure is by using a Tyre Pressure Monitoring System or TPMS.
What is TPMS?
This is an electronic system in your vehicle that monitors the tyre air pressure and alerts you when it falls low. It warns you that one or more tyres are significantly under-inflated which might lead to unsafe driving conditions.
The TPMS sensors in the vehicle show a warning light when the tyre pressure drops to 6-7 PSI. The low tyre pressure indicator of TPMS is a yellow symbol that illuminates on the dashboard instrument panel. It is in the shape of a tyre cross-section with an exclamation point.
History of Tyre Pressure Monitoring System (TPMS)
Tyre pressure monitoring systems were first adopted by the European Market in the 1980s. It was an optional feature for luxury passenger cars.
After an initial appearance on the low-production and expensive 1987-89 Porsche 959 supercar, TPMS was a mandatory feature on all 1991 Chevrolet Corvettes.
Eventually, tyre pressure sensors slowly began to increase in popularity on more expensive performance cars. In the coming years, it became a part of all the cars.
How Does Tyre Pressure Monitoring System Work (TPMS)?
You might think that TPMS works the same way in all the vehicles but that is not the case. The illumination of the low tyre pressure is the final step of either Indirect TPMS or Direct TPMS.
Let us look into these in detail.
Indirect Tyre Pressure Monitoring System (TPMS)
As the name implies, indirect TPMS does not use a direct 'PSI' reference to calculate tyre pressure. The system estimates tyre pressure differentials based on wheel and vehicle speed and the tyre size. This system piggybacks on the anti-lock braking system (ABS) and traction-control system. It uses the information from these sensors and determines if the individual tyre is underinflated.
The radio frequency signals from each tyre-mounted sensor are transmitted to a central receiver. Here, the individual air-pressure readings are compared to the manufacturer's recommended inflation pressure.
If the pressure in any tyre drops under 75 percent of the manufacturer's recommended calibration, then the warning light will illuminate. Some manufacturers even display the actual pressure on each tyre in the driver information centre.
The idea behind indirect tyre pressure monitoring system(TPMS) is that the circumference of a tyre decreases slightly as it deflates and the rolling resistance increases. The system uses the individual wheel-speed sensor information and detects the difference between an underinflated tyre and a properly inflated tyre. The onboard software will then calculate the difference that exists between the wheels and determines the percentage of underinflation based on the manufacturer's recommended tyre size. It will trigger the warning light at the 75 percent threshold.
Advantages of Indirect Tyre Pressure Monitoring System (TPMS):
- Requires less programming and maintenance over the years
- Affordable as compared to a direct TPMS
- Less overall installation maintenance than direct TPMS
Disadvantages of indirect Tyre Pressure Monitoring System (TPMS):
- Must be reset after a routine tyre rotation
- May be unreliable when the tyres are unevenly worn out
- May become inaccurate if you purchase a smaller or bigger tyre
- Must be reset after inflating each tyre properly
Direct Tyre Pressure Monitoring System (TPMS)
A direct Tyre Pressure Monitoring System (TPMS) measures a tyre's actual pressure and such systems are usually accurate to within 1 psi. All the current direct TPMS use a gauge that is mounted to the wheel or tyre valve. This gauge will send a signal to the car's computer. The data interrupted and displayed in the car depends on whether it is a low-line or a high-line unit.
The high-line system has sensors that are mounted in each of the wheel wells and it displays the individual pressure of each tyre. On the other hand, the low-line systems are found on less expensive cars and they will prompt only the low-pressure warning signal. Once you see the illuminated signal, you will have to figure out which tyre has low pressure.
If you want the systems to actually display the pressure of each tyre, go for a car with a high-line system.
Advantages of Direct Tyre Pressure Monitoring System (TPMS)
- It sends the exact tyre pressure
- Isn't prone to inaccuracies that can be a result of tyre rotations or tyre replacements
- Easy and simple resynchronization after tyre rotations or replacements
- Sensor batteries have a long life and can last a decade
- Can be used in the spare tyre of the vehicle
Disadvantages of Direct Tyre Pressure Monitoring System (TPMS):
- More expensive than indirect TPMS
- Sensors are prone to damage during mounting or demounting
- When the battery is dead, the whole sensor has to be changed
- Though the resynchronisation is easy, it requires expensive tools
What to Do When the TPMS Light Comes On?
As soon as the TPMS light illuminates, check the pressures on all the tyres. Chances are that only one tyre may need air, but it is a good practice to check all the tyres. If the light is flashing, it may indicate a malfunction with the TPMS system. It could also mean that you are using a spare tire and the vehicle is unable to detect the sensor of the original wheel.
Another factor that may affect the tyre pressure and trigger the TPMS light is the temperature. When the weather is cold, the tyre pressure will drop. There could be a loss of about 1 psi when the ambient temperature drops by 10 degrees. When you first start up the car after a cold night, the TPMS symbol might illuminate for a short time and then shut off.
If it persists, check the tyre pressure immediately.
There you go, you know all you need to know about the Tyre Pressure Monitoring System. So, the next time it blinks or illuminates, you know exactly what to do. Make sure the tyres are at the right pressure to maintain safety and prolong the life of the tyres. Do not drive on underinflated tyres at any cost.