Introduction A tyre pressure monitoring system (TPMS) is a safety feature that continually monitors a vehicles’ tyres and alerts the driver to changes in tyre pressure. The changes in pressure can be detected by either direct or indirect means.
Indirect TPMS This is generally fitted to a vehicle that has had fitted or can be fitted with run flat tyres. This is because it is difficult to see or feel deflation in this type of tyre. Indirect tyre pressure monitoring systems do not use pressure sensors to monitor tyre pressure, they work from the ABS or speed sensors on the vehicle. Indirect systems monitor tyre pressure by assessing the rotational speeds of each tyre, and work on the premise that an under-inflated tyre has a slightly different diameter than a fully inflated tyre. An algorithm is used to assess the differences in wheel speeds. The under-inflated tyre would therefore rotate at a different speed than the correctly inflated one, causing a tyre pressure warning. The deflated tyre is not identified, the driver has to check all 4 tyres.
Indirect TPMS operation
Negative aspects of indirect TPMS
- The system is not very accurate.
- When tyres are re-inflated, the system needs to be re-calibrated.
- When tyre positions are changed, the system needs to be re-calibrated.
- When the tyres are replaced, the system needs to be re-calibrated.
- The system can be re-calibrated by the driver without first ensuring that the pressure is correct in all tyres.
- A puncture after parking is not immediately identified.
Tyre pressure monitoring and the law in Europe
- From November 2012 all new type vehicles in the M1 category (vehicles under 3.5 Tonnes with less than 8 seats) will be required by law to have TPMS installed. This applies to the road wheels not the spare.
- By November 2014 all new passenger vehicles will have to have TPMS installed by the manufacturer.
The law is not currently retrospective, and does not apply to older vehicles. Many car manufacturers have already introduced TPMS to their vehicles ahead of the 2012 legislation change. More and more cars now have TPMS already fitted. Showrooms are full of TPMS compliant cars. This law applies to passenger vehicles only, with no more than 7 seats.
(Source: Continental Tyres)