An arrangement for monitoring the under-inflation of one of the tires of a ehicle comprising a chassis and at least one axle having two wheels equipped with tires, based on an analysis of the differences in position of the wheels relative to the chassis, characterized by the fact that the measurement of the differences in position of the wheels on the same axle relative to the chassis is effected by means of an element of generally U-shape, the central portion of which has a fixed position relative to the chassis of the vehicle, and each of the ends of which are connected to one of the wheel holders of the wheels of the axle in such a manner that any difference in position between the two wheels relative to the chassis of the vehicle results in a twisting of said element.