TPMS working party risks safety, CO2 reduction

ERJ staff report (DS)

Geneva -- A UNECE committee risks endangering road safety and creating unnecessary CO₂ emissions at a key meeting in Geneva next week. The committee is set to debate technical details of a new EU law which will require all new cars to have a factory-fitted tyre pressure monitoring system (TPMS) from November 2012.

Last March, the European Parliament passed a law requiring new cars to be fitted with an accurate TPMS system. The law was designed to reduce Europe's CO₂ footprint and to improve road safety. It is due to be ratified by the Council of Ministers next week. Even as the Ministers sign the law onto the statute books, however, the intent behind it could be undone at a detailed technical meeting in Geneva.

The regulation did not specify any detail about the technical requirements of the proposed TPMS systems. That is left to the UNECE, which has the relevant expertise and is also accessible to countries outside the EU.

For the last two years, experts on the UNECE panel -- the GRRF for brakes and tyres -- have been thrashing out the fine details of the system and how it should be tested and operated. The working party has devolved into two main groups. On one side are the car makers who want to ensure that the technical specification allows the cheapest possible system to be fitted. On the other side are the tyre makers and component suppliers who want to ensure safety and CO₂ reduction are paramount.

An under-inflated tyre uses significantly more fuel -- and hence leads to more CO₂ emissions -- than a correctly inflated tyre. It is also less safe when carrying heavy loads, or when cornering.

Currently, the car makers have suggested that the system need not give any kind of warning for up to an hour, if more than one tyre is under-inflated. The tyre makers say this is too long. Currently the average passenger car journey time in the EU is around 20 minutes. A limit of 30 minutes, let alone 60, would make the system useless on the majority of car journeys, leaving most cars free to emit more CO₂ than necessary, with no warning to the driver.

Furthermore, the US has for over a year, had in place legislation which requires all new cars to have TPMS systems fitted as standard. These have a safety limit of 20 minutes for detecting an under-pressure situation. The Chinese transport authorities are proposing a 6 second detection time.

Technically, it is easy to make systems that can detect a low pressure situation within a few seconds. However, that speed of reaction costs. A fast-acting system (so-called direct system) costs around euro 25 per vehicle, with no costs over the lifetime of the vehicle. An equivalent slow-acting system can be implemented for around euro 8 per vehicle, but takes a long time to react and imposes extra costs on the owner of the vehicle, as the tyres must be replaced with specific -- and expensive -- products each time they wear out. That extra cost --placed on the owner -- is far more than  the €25 per vehicle that the vehicle maker needs to fit a safe, effective TPM system.  

The EU regulation say the TPMS specification must be technology-independent, that is to say must not require a direct or indirect system. It must, however, be accurate and effective. Car makers are arguing that the indirect systems are effective, despite being slower, costing more for the consumer and potentially inaccurate.

Two key research programmes show that the cheaper, slow-acting indirect TPMS systems are at best useless (see links below) and at worst positively dangerous, as they give drivers a false sense of security. Direct TPMS systems, however, have a marked effect on CO₂ emissions, fuel consumption and safety.

Worse, it is easy for a driver, through ignorance or lack of awareness, to set up an indirect system to show a safe condition, even when one or more tyres are severely under-inflated.

WP29 meets in Geneva next week from 23-26 June. It will deliver a recommendation on pressure limits and on the time. The tyre industry says it has already made a big compromise by allowing a time limit for multiple pressure loss of 30 minutes. It is completely unacceptable for both safety and CO₂ emissions, they say, to extend this any further. 

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Tire Pressure Maintenance-A Statistical Investigation from NHTSA

TPMS TF Conclusions V04.pdf