Staying cool under pressure
There are two types of tire pressure monitoring systems, (TPMS), that were mandated in the the Federal Motor Vehicle Safety Standard to help prevent the problems of under inflated tires and the subsequent failure of those tires. You will find these on all later model vehicles.
The first type is referred to as a “direct” TPMS. Those types of systems have a sensor in each wheel and send a signal to a receiver in the vehicle. In this situation, when any of the tire pressure drops (25%) below the recommended cold tire inflation pressure, (indicated on the sticker of the vehicle), the indicator will let the driver know. Besides information on a gradual loss of pressure, it will give you a quick indication of a puncture that would cause a complete, quick loss of air.
Another type is called an “indirect” TPMS. This works with your anti lock braking system, (ABS) comparing wheel speed and the rotation of one tire to another. In other words, if one tire is low, the changes to that one tire will actually cause a difference in revolutions. These differences are measured through the ABS and once again, the driver will receive the information on the indicator.
BMW products actually use both types of systems, depending on your model and year of vehicle.
Remember, there is nothing that takes the place of checking your tires pressure on a monthly basis or before a long trip. Always look for the recommended tire pressure on the sticker/placard on the drivers door pillar. Pay attention to any load factors and remember to check the pressure when your car is “cold”. You may have to reset your TPMS at your dash, also.