Abstract: A pressure relief valve for a tire rim in which a valve body has first and second chambers separated by a restricted passageway of reduced dimensions. The valve body has an inlet connected to the first chamber, and an outlet connected to the second chamber, and can be mounted in a suitable opening in a tire rim with the inlet exposed to pressure within the tire and the outlet exposed to the atmosphere outside the tire. A valve member is normally located in the first chamber and is seated against a seat at the entrance to the restricted passageway by air pressure within the tire acting on it via the inlet, sealing the outlet. Either the valve member or the walls of the passageway, or both, are made of deformable elastomeric material so that when the air pressure rises above a predetermined safety level, the ball is forced through the passageway into the second chamber into a position in which air can flow past the ball and out through the outlet, reducing the internal pressure in the tire.