Why can't I use run-flat tires without a Tire Pressure Monitoring System (TPMS)?

A feature of the stiff sidewalls found on run-flats is that they never look flat. As a result, the danger of driving on underinflated tires is even greater, as many people don't check their tire pressure until tires "look" low. To counter this problem, the use of tire-pressure monitoring systems (TPMS) has become mandatory in run-flat applications. Since run-flats only provide a limited zero-pressure driving range, TPMS is critical to help the driver know when the mileage clock starts ticking, and more importantly, when time is up.