Opinion ID: 783159
Heading Depth: 2
Heading Rank: 1

Heading: Indirect TPMSs

Text: 18 Current indirect TPMSs work with a vehicle's ABS [anti-lock braking system]. The ABS employs wheel speed sensors to measure the rotational speed of each of the four wheels. As a tire's pressure decreases, the rolling radius decreases, and the rotational speed of that wheel increases correspondingly. Most current indirect TPMSs compare the sums of the wheel speeds on each diagonal (i.e., the sum of the speeds of the right front and left rear wheels as compared to the sum of the speeds of the left front and right rear wheels). Dividing the difference of the sums by the average of the four wheels [sic] speeds allows the indirect TPMS to have a ratio that is independent of vehicle speed.... If this ratio deviates from a set tolerance, one or more tires must be over- or under-inflated. A telltale then indicates to the driver that a tire is under-inflated. However, the telltale cannot identify which tire is under-inflated....