Markus

Ok, so this could be a generic question as I'm sure the system used is generic.

Anyway, You can get the S4 with a tire pressure monitoring system, am guessing the display between the tach and speedo is where this info would be displayed.

The question is, how does the system actually work? I would assume for it to work there have to be sensors inside the wheel rim to be able to measure the pressure.

The real point here is this. If I wanted to swap wheels (and I would, as I'd have one set of wheels for summer, one for winter) then I guess I'd either need to move the sensors over (sounds like a pain to me) or purchase another set and get them fitted when I get the second set of wheels and tyres.

Dick Cheese

There are no sensors inside the wheel. The systems I've heard of use the axle of the car to transmit a weak radio signal and a sensor in the wheelarch to receive the signal. The fall in pressure will result in less-dense air between the transmitter and receiver, and the radio signal received increases in amplitude. The system does not tell you your actual tyre pressures, it just warns you if there is a drop in pressure from your set value. You can use any wheels you like, but you'd have to reset the tyre pressure monitor after fitting the new wheels.

carl

There's a similar system on my wife's 3-series Beemer. I believe that it detects differential rates of deflation, so if you blew out all four tyres simultaneously it wouldn't know. I think it somehow compares the values for each tyre, and if one is out then it flags the warning. As Mr Cheese rightly says, every time you inflate the tyres you have to reset the monitor.

russell hayward

Had it on my M3, absolutley pointless in my opinion, assuming you can be bothered to check your tyres regulalry.

Right pain having to reset all the time as well.

Newbie123

I don't know if the system in the S4 is the same as the one in the A8, but that system actually does have sensors within the wheel (tyre valve to be precise) and it actually tells you the individual pressure of each tyre including the spare, with the information being displayed on the Sat Nav screen, the DIS between the speedo and rev counter displays warnings of any pending deflation. It's a £500 option on the A8.

Don't know if that helps.

logiclee

There is also another VAG tyre pressure monitor that measures rpm of the tyre. You calibrate it when the tyres are at the correct pressure, when a tyre drops a little pressure it increases rpm in relation to the other three and you get a warning.

Not sure which system is fitted on the S4

Lee

Skittles

The BMW M3 system is cr@p: it measures relative rotational speeds of each tyre. It always goes off when it shouldnt and never when it should.

I have an Audi RS6 (don't know if this is the same system as the current A8 somebody mentioned) and it transmits a signal via I think the valves and it actually seems to work. I had a warning the other day and sure enough I was 2 psi down.