Tire pressure monitoring

[rocktheroad]

How it works? Or better does it works at all? I know this is cheaper ABS/ESP version, but I haven't noticed that they TPM works. Last weekend I have been checking tire pressue, adding 0.2-0.5 bar to all four tires. I forgot to press and hold TPS button but never got warning that pressure changed.

Anybody seen thos working?

[ddyer79]

It does not monitor pressure, it measures the speed of the wheel by using the Anti-lock braking sensors. Basically, as the tyre deflates, it has a smaller circumference and hence turns faster than the wheel on the same axle. Once beyond a certain speed differential, it flags an error.

Generally there needs to be a 4 to 5 psi drop in pressure for it to register. I found it very effective in handling info on a slow puncture I had.

Hope this helps.

[lowedb]

I've seen it working on my previous Superb, and another car too.

[Neily03]

Basically, as the tyre deflates, it has a smaller circumference and hence turns faster than the wheel on the same axle.

I'm not sure that's entirely true, while yes the smaller radius from the centre of the wheel to the road means in theory it would turn faster the fact that the tyre is under inflated means the wheel turns slower due to the increase friction (hence an under inflated tyre get hot)

[lowedb]

No, the friction doesn't cause it to turn slower. If that were true it would wear out superfast, like in a few tens of miles. The circumference doesn't change that much(it's got steel bands in it remember), but the hub is less central so the effective rolling radius reduces. The effect is exactly the same though, it's as though the circumference has reduced.

In fact the reason an underinflated tyre gets hot is the flexing of the sidewall. Because it flexes a lot more the internal friction in the rubber heats it up. That's why it's such a problem, this heating and flexing can cause the whole carcass to overheat and delaminate.

[wokwon]

Note that it only detects when the rotation speed is different per axle. If both tyres on the axle deflate at the same speed, the warning will not be triggered. Likewise, if all four tyres deflate the same the warning will not be triggered.

It works well and I have had it trigger on a loss of 5 lb in^-2 (about 35kPa).

[Phil_P]

Worked on my Passsat when I had a puncture. Put the spare wheel on and the warning light triggered. Checked/adjusted the pressures and reset by holding the button.

I think it triggers when two wheels on the same axel differ by ~3psi or more. It's not always instant - you might have to drive a few miles before the light will come on.

[adstalker]

I have had it come on when I had a puncture in one of the rear tyres. It was a slow puncture so I pumped it back up and reset the monitor. The monitor triggered again and when I checked the tyre pressure it was 0.2bar lower than what I had set it to when I re-inflated the tyre.

I have also noted that the it triggers when the tyre preasure increases. When I still had my wintre tyres on, I did a long journey on a hot day and the tyre pressure increased by about 0.2bar in all tyres which triggered the monitor.

[Hillhound]

I have had it trigger 3 times in 2 years in my Superb Estate. Twice for slow punctures because of nails and once when I had attached a heavily laden caravan. Found it to be reliable!

[Optimist]

I have just added a comment in a different thread re-towballs. However, I used my caravan for the first time this year with my new Superb Hatchback 4x4 170 and I forgot to increase the tyre pressures (something I normally always do when towing). It wasn't long before the tryre pressure warning light lit up and this due to the extra weight of the caravan.

I pumped the tyres up to the correct pressures, reset the TPM and all was well from then on. Now I am back home I've put the tyres back to the correct pressures.

By the way, I have a pressure gauge on my foot pump but have always thought it was inaccurate, so I bought a new gauge from E-Bay (Race-X Professional Pressure Gauge) , recommended by Autocar Express and discovered the foot pump is out by 0.4 Bar (almost 6 psi). Thats a big difference!

[majland]

Unfortunately i've also tested it a few times. We have had 4 flats in a year :-(

It takes a while to register the change so if you get a slow puncture, park and then drive on later in the day you may be driving for a few km before you get the warning and might be driving almost on the rim (happened once).