Abstract: A mounting plate is provided to extend along beneath and to be secured to one end of a transverse axle adjacent a pneumatic tire journaled from the axle end and the plate includes structure whereby different size U-bolts may be utilized in conjunction therewith for clamping the plate to the underside of axle housings of different diameters. An actuating switch is provided and is mounted from the plate for adjustable positioning laterally of the associated axle housing and the switch includes a depending 360 degree wobble actuator for contact with the ground closely adjacent the point of contact of the tire with the ground or contact with the adjacent side wall portion of the tire when the latter becomes deflated.