Asking for a neighbour and to satisfy my curiosity.
My elderly neighbour tried to use the Asda air pump the other day but this time failed due to his health, been in hospital recently.
So to the rescue I offered to pump his tyres up to the correct level as his TPM on his Vauxhall is showing low on 3 tyres. Using my trusted air pump and gauge set them at 30psi. He checked his display and it was showing more air in but not quite the correct amount.
Question is how accurate are these TPM’s and will it reset itself once he’s driven the car. Asking as I’ve never had a car with TPM before.
Thanks all.
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I can only answer from my experience of a Honda CR-V with TPM. Once the correct tyre pressures are set the system has to be initialised so the car knows what the correct pressures are. It then judges against that setting. I only learnt that after inflating the tyres one day and then on the first journey afterwards the tyre pressure alarm went off. Hopefully other makes are different as it’s a cr*p system.
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It depends what or how pressure is monitored. If it using the ABS system to detect wheel speed then it does not actually know the pressures, just that different wheels are turning at different speeds due to diameter differences across the tyres. If they are the actual bolt in TPS units then they are pretty accurate, if functioning correctly. and certainly a match for any typical tyre inflator. There are then two types, as far as I know, ones that need to be driven a mile or so to pick up their position and pressure. Or ones that are required to be told where they are on the car and work from there. However, some systems then interrogate these every minute or so and will display a pressure even when static. In either instance though you either need to drive or wait until the pressure updates.
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Thanks Nick for explanation and others in the thread
I know the owner has varying tyre brands on the car, new and old mixed tyres and not necessarily matching on each corner either. Something I pointed out to him upon purchase, they are tyres with tread as far as he’s concerned.
Anyways I’ll go check on him and his car again later see how both are doing.
Many cars haven’t liked mismatched tyres since maybe early 1990s when ABS etc was introduced to mass production cars. The four tyres should really be a matched set if using TPMS/ABS for monitoring them.
My Vextra-B complained when I was running the spare after a puncture. All four tyres had identical circumference, but the odd never-used spare (OEM Goodyear ) had a different rolling resistance to the three newish Dunlops. New Dunlop arrived eventually and the problem vanished.
Brother in Law’s Polo does not like the brand-new tyre replacing a punctured spare. The other three should have been changed too as they were near the wear limit when I checked it for him.
By contrast, his son’s BMW’s TPMS is also complaining about its tyres; all four looked to be the same type of Pirelli, and with identical pressures and identical circumferences and tread depths near 7mm, all measured by me, but no two with the same ages. They were a recent fitting of a “new” job lot from “a mate at the tyre place” with a date spread of six years, 2016 to 2022!
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