8th April 2017

Fleet drivers and managers encouraged to heed tyre pressure monitoring warnings after a 212% rise in TPMS-related MoT failures

As with pretty much all automotive technology features, whether relating to entertainment or, more importantly, safety, it was the sports and luxury car sector that had the first bite at tyre pressure monitoring systems (TPMS) back in 1986, with the Porsche 9591. Car historians unanimously agree that the 959 was a technological tour de force, and we’re primarily interested in the way it boasted the world’s first production incarnation of a TPMS, in the form of hollow magnesium alloys incorporating a centralised tyre pressure monitoring system along with inflation/deflation ability2.

In the 1990s, it was mainly French car manufacturers who had the bit between their teeth in developing refined TPMS, with Renault basing its system on PAX from Michelin, the brand’s endeavours culminating in the Laguna II being launched as the first mid-size, high-volume production car to come fitted with one as a standard safety feature. Fast forward the clock and, while BMW still has a penchant for run-flat tyres, TPMS have become a legal requirement, proving really handy and protective for private and business motorists by displaying or even audibly communicating a warning when the pressure of one or more tyres becomes abnormal.

Two different types of TPMS exist, to somewhat confuse matters. The first breed is the direct system, which involves a sensor on each wheel, engaged in physically and continuously measuring the pressure, transmitting this data back to an often dedicated ECU and displaying and/or sounding a warning if deemed appropriate. Aside from the reliance on batteries impairing direct TPMS slightly, along with steep repair costs, and their susceptibility to dirt, adverse climate conditions and physical knocks, direct tyre pressure monitoring systems (dTPMS) are unarguably the most accurate solution, and some vehicles even allow their drivers to permanently display pressures on the dashboard or instrument panel in real-time. This can prove fascinating, clearly showing how pressures drop when speed is reduced, and vice versa.

The other main type of TPMS is an ‘indirect’ system, whereby specific tyre pressure sensors are not fitted to each wheel, the vehicle instead relying on data from its Anti-Lock Braking System (ABS) to indicate probable falls in pressure. A tyre’s diameter will reduce slightly if it has lost air for whatever reason, from a straightforward puncture to a bad bead seal between it and the alloy wheel, and indirect TPMS simply compare wheel speeds to identify culprit tyres and warn drivers if a 25% or greater drop is detected.

The advantages of indirect TPMS are that they are significantly cheaper to integrate and make life easier for private motorists and fleets who swap wheels every so often, such as when exchanging summer tyres and wheels for winter, or as part of scheduled fleet maintenance. The drawback, though, is that because they use relative ABS wheel speed values, indirect TPMS won’t alert drivers if the pressure of all the tyres has dropped by approximately 25% or more3. Additionally, an iTPMS can’t monitor tyre pressure of a stationery vehicle, so isn’t ultimately as safe as a direct system which would theoretically warn a driver against setting off in an unsafe car.

Indirect TPMS have made a comeback in recent years, though, with VAG making a concerted effort back in 2011 to improve the intelligence of their systems, most notably on Audi models4. BMW, Honda and Lexus have also focussed on indirect implementations of late, as have more and more car manufacturers, in the wake of TPMS installation becoming mandatory law across the EU in November 2014. Over in the United States, meanwhile, it is federal law for vehicles to incorporate a TPMS that notifies the driver of a 25% drop in pressure.

As reported by motoring journalist Neil Briscoe in the Irish Times7 last week, pressure group Transport & Environmental (T&E) have carried out independent testing of various cars and found, for example, that the indirect TPMS in the latest Fiat 500 and Volkswagen Golf failed nearly all the real-world tests they were submitted to. Julia Poliscanova from T&E expressed deep concerns to the Irish Times, saying: “Manufacturers could be deploying similar defeat devices to get ineffective tyre pressure monitoring systems to pass safety tests and save themselves €10. Investigations of the suspicious TPMS performance must be carried out. Our tests clearly show that the unsafe indirect systems put drivers, pedestrians and cyclists at greater risk of dangerous blow-outs.”

Against a backdrop including 112 serious RTAs and 14 fatalities in the UK during 2015, caused by incorrectly inflated tyres5, TPMS are a key element in maximising tyre life, fuel efficiency, vehicle uptime, road safety and environmental greenness. A poll conducted for AA Tyres in March 2017 found that 27% of the 20,000 participating motorists hadn’t checked their vehicles’ tyres pressures for a couple of months, with an estimated 2 million UK drivers leaving this basic task for as long as six months each time. Concurrently, Enterprise’s recent survey of grey fleet drivers as published in Fleet World identified that 57% don’t check the tyre pressure of their typically older and less safe vehicles6.

As a telematics, insurance and automotive technology business heavily involved in the company car world, a TPMS-related headline in FleetNews in March 2017 caught our eye8, the article documenting how MoT failure rates due to tyre pressure monitoring system issues more than trebled from 2015 to 2016, with over 23,000 UK vehicles requiring remedial TPMS investigations before being presented for a retest.

TyreSafe’s Chairman, Stuart Jackson, told FleetNews: “TPMS adds significantly to general tyre safety making it easy for the driver to know if their pressures aren’t at the right level when out on the road. But, clearly, even though Britain’s motorists are being warned there’s a safety issue they’re choosing to ignore it. Regrettably, this leap in MOT failures due to TPMS defects underlines that a poor attitude to tyre safety is not an issue exclusively associated with older vehicles.”

With grey fleet vehicle usage still widespread in the UK, we agree with TyreSafe that tyre safety and the correct functionality of TPMS should be treated more seriously by fleet managers and also drivers themselves, with any TPMS concerns or issues reported and addressed promptly to keep road users and indeed pedestrians safer.






1 https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system

2 https://www.motor1.com/news/63301/kimble-kutaway-porsche-959/

3 http://www.tirereview.com/indirect-tpms-imports/

4 http://bestride.com/news/technology/audis-indirect-tire-pressure-monitoring-system-why-it-makes-good-sense-with-awd

5 https://inews.co.uk/essentials/lifestyle/cars/car-news/8-million-drivers-risking-safety-dangerous-tyres/

6 http://fleetworld.co.uk/barometer-february-2017/

7 http://www.irishtimes.com/life-and-style/motors/penny-pinching-on-tyre-tech-is-putting-lives-at-risk-1.3021608

8 http://www.fleetnews.co.uk/news/manufacturer-news/2017/03/06/concerning-rise-in-mot-failures-due-to-defects-with-tyre-safety-system