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Originally Posted by geckoGT
The Mini ones on the R56 are not actually a sensor in the wheel, they work on a change in rolling diameter due to a deflated tyre as picked up from the ABS sensors. |
It's still operating via a sensor. Some have the sensor in the wheel itself some via the braking system. The can still be easily damaged and the cost of the sensor varies depending on the car. My quoting was a general overview, as I wasn't wasting 6 pages going through each and every car fitted with them, where they were fitted and the cost of replacement of them.
There is also an aftermarket system available, where by the sensor is the valve cap and sends a signal to a devise inside the car and reads the pressure. (Tyre dog is the name). The problem with that system is, little mongrels that nick valve caps, means you have to buy a complete new system @ $400 to $500 a pop.
I have also seen valve caps that are preset to 32 to 34 PSI. These show a green piece when the pressure is at this maximum pressure. This green section disappears if the pressure drops below that, but that system requires you to actually look at the valve cap. Again, little mongrel kids can pinch them.
There are also valve caps for truck tyres. These are preset to work between 70 and 130 PSI. Once the pressure drops below 70 PSI, it has a little red led light that flashes continuiously until you pump it back upto the right pressure. Again, this requires you to actually look at the valve cap and little mongrel kids can pinch them.
So there are various systems around, but the cost and how they work vary.