Direct vs Indirect TPMS

Direct (‘dTPMS’)

This type of system uses individual pressure sensors mounted inside each wheel. Each sensor sends its signal to the vehicle via a live, wireless connection. In Europe, the transmission frequency of direct sensors is 433MHz.

Advantages

  • Fast reacting to changes in tyre pressure – typically only taking a few seconds.
  • Highly accurate – measuring to 1 or 2 psi.
  • Will detect a puncture, even after parking.
  • Will detect a slow leak.
  • Able to identify specific locations of pressure issues.

Disadvantages

  • Requires maintenance/servicing, using specialist tools and equipment.
  • Risk of damage to sensors when tyres are removed.

Indirect (‘iTPMS’)

This type of system does not directly measure the pressure in the tyre, but uses the ABS sensors on the vehicle to assess the rotational speeds of each wheel. An under-inflated tyre will have a slightly different diameter than a fully-inflated tyre, resulting in that particular wheel having a different rotational speed. This information is then sent to the vehicle’s on-board computer, which triggers the TPMS warning light.

Advantages

  • Technology already installed on vehicles.
  • Doesn’t require servicing or the need for special tools.
  • No risk of damage when removing tyres.

Disadvantages

  • Generally not as accurate as direct sensors.
  • Slow to react – vehicles often need to be driven for a considerable amount of time before the TPMS warning light comes on.
  • A puncture after parking may not be immediately identified.
  • Since tyres lose pressure naturally, roughly at an equal rate – this can result in all four tyres being underinflated, without the warning light coming on at all.
  • Some indirect systems do not work well with non-OE replacement tyres, requiring specific tyres to be installed for the system to work properly.
  • Requires recalibration by the driver every time a vehicle’s tyre pressure is adjusted or a tyre is changed.