Tyre pressure plays an important role in vehicle handling, tyre wear and driving safety. Modern vehicles may use a Tyre Pressure Monitoring System (TPMS) to alert the driver when tyre pressure appears to be too low.
There are two common approaches: direct TPMS and indirect TPMS.
What Is Direct TPMS?
A direct TPMS uses pressure sensors, usually installed inside the wheels or attached to the tyre valves, to measure tyre pressure.
The sensor transmits information to the vehicle's monitoring system. Depending on the vehicle, the driver may see a warning light or individual tyre-pressure readings.
Advantages
- Measures tyre pressure directly.
- Some systems display pressure readings for individual tyres.
- Can identify pressure loss without relying solely on wheel-speed differences.
Limitations
- Sensors have batteries that eventually need attention.
- Sensor replacement and servicing may require specialised equipment.
- Wheels must be handled carefully during tyre replacement to avoid damaging sensors.
What Is Indirect TPMS?
An indirect TPMS generally uses wheel-speed information from the vehicle's anti-lock braking system.
A tyre with lower pressure may have a different rolling circumference from a properly inflated tyre. The system analyses wheel behaviour and looks for patterns that may indicate pressure loss.
Advantages
- Does not require a separate pressure sensor inside every tyre.
- Can use existing vehicle sensor systems.
Limitations
- Does not directly measure air pressure.
- Performance depends on the system's design and calibration.
- Some systems require recalibration after pressure adjustments or tyre changes.
Why Correct Tyre Pressure Still Matters
TPMS is an alerting system, not a replacement for routine inspections. A warning may appear only after pressure has fallen sufficiently, and not every tyre problem produces a warning.
Drivers should check tyre pressure manually at the intervals recommended by the vehicle manufacturer and investigate recurring warnings.
Never ignore a warning simply because it disappears after restarting the vehicle.
Final Thoughts
Direct and indirect TPMS use different methods to identify possible pressure problems, but both are designed to help drivers notice conditions that deserve attention.
Understanding which system your vehicle uses can make its warnings easier to interpret. Always consult the vehicle handbook for the correct pressure specifications and recommended maintenance procedures.
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