Fig. 224.-Showing One Advantage of Sectional Block Tire Design Over Continuous Tread Type. bration in every direction and prevent concentration of the load on one portion of the tire as would be the case if separate blocks were used. The separate block construction, however, has an important advantage in that it permits of replacing one or more defective blocks without necessitating the renewal of those which have not been so severely punished. It is claimed that very often a one-piece tire will be so badly cut or bruised at one point that it will have to be removed for repairs even though the rest of the tread is not affected. In a sectional or block tire only the injured portion would have to be replaced, which means more economical maintenance because of easier installation. Fig. 225.-Leading Forms of Cushion Tires. A-Motz. B-Swine hart. Q. What other materials besides steel and rubber have been used for motor vehicle tires? A. Experimental tires have been made composed of wood with the fibers or grain running parallel to the spokes and have given satisfactory service in certain applications. Various textile fabrics have also been tightly compressed together to form a practically solid mass and have been tested and found satisfactory. It is claimed that wood or textile fabrics offer a greater degree of resiliency than a steel tire and have a traction effort or friction grip on the ground equal to a rubber tire operating under favorable conditions. It is claimed, also, that these provide superior traction to rubber in muddy roads or on wet asphalt. Q. What is a cushion tire and on what vehicles are they com monly used? A. Cushion tires are a composite form intended to provide more resiliency than solid tires and at the same time eliminate the troubles incidental to the use of inflated members. Two methods of obtaining a cushion effect are outlined at Fig. 225. The tire shown at A is a twin tread form composed of very resilient rubber compound, provided with a series of notches cut around the tread as indicated at A and attached to the rim by means of bridges of compound separated by air spaces B. When a tire of this construction passes over an obstruction B, it can deform considerably on account of derangement of tread and supporting members and the wheel does not ride over the obstacle, as would be the case if the tire did not Fig. 226.-Typical Cushion Tires Showing How a Certain Degree of Resiliency May Be Obtained Without Air. give to any extent. In the tire shown at B, the resiliency is obtained by breaking up the mass of rubber by a large number of holes which permit of greater flexibility. Cushion tires are generally used on light delivery wagons or electric automobiles. They are suitable only for slow or moderate speed vehicles, as they are not sufficiently resilient to cushion the mechansim from the shocks incidental to high speeds. Q. What is an "airless" tire? A. The term "airless" tire is synonymous with cushion tire and includes all forms in which resiliency is obtained by peculiar tread formation or air substitute filling instead of by compressed air. Various forms of airless tires are shown at Fig. 226. That at A is the simple cushion form of the twin tread type moulded of resilient rubber compound. The form at B is known as the Dayton "airless" tire and resembles the conventional form of clincher casing, the exception being that the load is supported by means of arches of very resilient rubber separated by air spaces which permit of distortion of the load carrying blocks. It is claimed that this construction offers important advantages inasmuch as the tread portion can be made of a tough, wear resisting compound whereas the more resilient load carrying blocks which are not subjected to ground friction can be made of softer and more easily deformed rubber composition. In both the forms shown at C and D, the pecul ar tread formation is depended on for resiliency. Q. Why are pneumatic tires necessary on most automobiles? A. Pneumatic or air filled tires are used on most automobiles because it has been demonstrated that the air cushion is the best shock absorbing medium known and the only one that is capable of taking the vibrations following in rapid sequence when a car is driven at speeds over fifteen miles per hour. Not only is it the easiest riding form but it insures longer life to the mechanism and also increased traction effect on practically all classes of road surfaces. Q. What is the usual construction of a pneumatic tire? A. Two forms of pneumatic tires are outlined at Figs. 227 and 228. The types that are generally used on automobiles are composed |