[Know when your tire has burst] TPMS tire pressure monitoring system | Which is indirect or direct? ｜DIY installation precautions

Hong Kong people commonly refer to tire pressure as "tire air", which means the gas pressure inside the tire. If the tire air is insufficient or excessive, the tire cannot support properly, causing deformation. Mildly, it affects ride comfort; seriously, it may cause handling problems with potentially serious consequences. If you want to learn more about tire air and tires, check out "Tire/Tire Brand Recommendations | 5 Major Types Introduction | Tire Replacement, Inflation, and Maintenance Tips".

In the past, checking tire pressure required manually using a tire gauge. In recent years, many new cars have built-in tire pressure monitoring systems, i.e., TPMS (Tire Pressure Monitoring System), which use sensors on the tires to collect data. If low tire pressure is detected, the TPMS warning light (horseshoe icon) will light up on the dashboard. TPMS mainly divides into indirect TPMS and direct TPMS. Although both are TPMS systems, their principles differ significantly.

Indirect TPMS

Indirect TPMS mainly uses the tire sensors in the Anti-lock Braking System (ABS) to measure the rotational speed of each tire. Since low tire pressure causes the tire diameter to shrink, the system compares the collected data with other tires and vehicle speed to determine if a tire has low pressure, and lights the tire pressure warning on the dashboard.

Although indirect TPMS requires no additional sensors, reducing maintenance costs for owners, it has drawbacks. Because it only uses tire diameter to judge low pressure, it cannot accurately measure tire pressure values. When low pressure is detected, it usually means the leak is already severe. Also, changing to wheels and tires of different sizes from the factory settings may cause data errors.

Direct TPMS

Direct TPMS installs sensors directly on the tires to read tire pressure status, so it is more accurate than indirect TPMS. It can measure tire pressure values and even read tire temperature. Direct TPMS is divided into two types - internal and external.

As the name suggests, internal TPMS installs sensors inside the tire at the valve stem, making them hard to notice externally. Factory-equipped direct TPMS systems use this type. Since sensors are installed at the valve stem inside the tire, repairs or maintenance require professionals to remove the tire. External TPMS installs sensors on the tire valve stem externally, which may not appeal to owners concerned about appearance but is easier to install and suitable for DIY.

Although many new cars come with factory TPMS systems, older vehicles may not, but owners can install TPMS themselves via DIY.

Generally, DIY TPMS systems only provide direct TPMS. The market mainly offers internal and external direct TPMS systems, including 4 tire pressure sensors and one display unit.

Installing Internal TPMS

It is recommended to have professionals install it because it requires removing the tire to replace the original valve stem with the pressure sensor. After installation, drivers can check tire pressure or condition from the display unit. However, some car models allow viewing tire pressure info directly on the original in-car screen by changing factory system settings, so installing a display unit may not be necessary. Note that changing factory settings might affect factory warranty.

Installing External TPMS

External TPMS installation is much simpler, just attach the sensor onto the existing tire valve stem. Users can easily install it themselves in just a few minutes. However, adding a sensor on the valve stem may look bulky and might not appeal to owners who care about aesthetics.

Also, users should pay attention to the display unit’s charging method. Some models have solar panels, but if the vehicle is often parked indoors, it may not get enough charge and require connecting a charging cable.