Patent ID: 7856870

Claim:
A method for alarming inner pressure lowering of tires comprising: receiving satellite electric wave utilized for GPS; detecting inner pressure lowering of tires utilizing information of the satellite electric wave; and detecting inner pressure lowering of tires utilizing wheel speed information; judging whether the judgment result of inner pressure lowering of tires detected in the detecting steps is adopted or not, wherein the step of detecting inner pressure lowering of tires utilizing satellite electric wave information comprises judging inner pressure lowering of tires from change in size of dynamic load radii by comparing an effective dynamic load radius with an initial value preliminarily stored as a dynamic load radius at a normal inner pressure, wherein the effective dynamic load radius is obtained by calculating an apparent dynamic load radius of a tire at running by successively comparing a calculated speed of a vehicle by a GPS device, in which the speed of the vehicle at running is calculated from information obtained by the GPS device, with a rotational speed of the tire obtained by a tire rotational speed detection apparatus installed on tire rotational portions of four wheels of the vehicle, and wherein judging the apparent dynamic load radius to be effective only when a running state is judged to be straight on a flat road at a constant speed from GPS positioning information.