Tyre pressure sensor

[RickS]

I wondered if they randomly go off as the tyre wears down so the radius is changing.

I'm just wondering what difference the tyre radius will make to the pressure? 

[SteveP]

^^^ The TPMS on UK cars works on the ABS sensors to detect changes in the rolling radius of the wheels.

[RickS]

^^^ The TPMS on UK cars works on the ABS sensors to detect changes in the rolling radius of the wheels.

OK Steve, but how does the ABS system measure the rolling radius?

[Ess_Three]

^^^ The TPMS on UK cars works on the ABS sensors to detect changes in the rolling radius of the wheels.

OK Steve, but how does the ABS system measure the rolling radius?

One revolution of a wheel gives x number of pulses detected by the ABS sensor...if all wheels give the same number of pulses per revolution when checked against the stored default (reset, once the pressures are set) then all tyres are at the same pressure...if one tyre goes flat, then it gives less pulses than the other 3 per revolution, or different value to the stored 'reset' value (over single or multiple revolutions, however the system measures it) it triggers the warning.

Same method for detecting wheelspin to activate XDS/traction control...same again for detecting locked wheels under braking etc.
Same principle again for launch control on aftermarket traction control systems or ECUs.

[RickS]

^^^ The TPMS on UK cars works on the ABS sensors to detect changes in the rolling radius of the wheels.

OK Steve, but how does the ABS system measure the rolling radius?

One revolution of a wheel gives x number of pulses detected by the ABS sensor...if all wheels give the same number of pulses per revolution when checked against the stored default (reset, once the pressures are set) then all tyres are at the same pressure...if one tyre goes flat, then it gives less pulses than the other 3 per revolution, or different value to the stored 'reset' value (over single or multiple revolutions, however the system measures it) it triggers the warning.

Same method for detecting wheelspin to activate XDS/traction control...same again for detecting locked wheels under braking etc.
Same principle again for launch control on aftermarket traction control systems or ECUs.

Of course, should have realised that, DOH!. Being pedantic, just one small point, wouldn't a flat tyre give more pulses than the others due to the reduced radius? [More turns to go same distance]

[Ess_Three]

Well spotted...yes, it would.
Difference in pulses being the key...once a pre-determined difference is met, it triggers the warning light and noise.

[ajmoir36]

http://www.my-gti.com/321/volkswagen-tyre-pressure-monitoring-system-tpms

[mfl]

^^^ The TPMS on UK cars works on the ABS sensors to detect changes in the rolling radius of the wheels.

We have the same set-up on the Aus version cars as well. sometimes its operation is a little random, I have had the warning go off after a bit of wheel spin, checked the tyres pressures and all was fine. Other times its gone off, there was between 2 - 6psi difference in the tyres.

[H12]

^ Was common on the mk5's too. I bet your dealer had not set it up 

Lol- it wouldn't surprise me !! Since I reset it, no more false alarms which is good but I did notice some very small stone chips on the 18" alloys when I checked the tyres... doh !! but can't say I'm that shocked juding by the state of the UK's roads 

[Snoopy]

^ Was common on the mk5's too. I bet your dealer had not set it up 

Lol- it wouldn't surprise me !! Since I reset it, no more false alarms which is good but I did notice some very small stone chips on the 18" alloys when I checked the tyres... doh !! but can't say I'm that shocked juding by the state of the UK's roads 

Little dab of lacquer on a cocktail stick to seal the hole, let it dry. Polish then jetseal109 them maybe some wax too.