Disc wheels are the answer to a demand for something better at a more reasonable price. The art of making wood wheels has been established, the machinery has become standardized and further reduction in cost is improbable; whereas the cost of suitable wood is steadily advancing and the trend, consequently, is upward. When the wire wheel was first introduced its use was a mark of distinction and to it can be traced the origin of the sport model, but its price cannot be reduced and it cannot compete, therefore, with the disc wheel on a price basis. The development of the disc wheel brought an equal distinctiveness of design and of pleasing appearance, but its progress has been different. The initial expenditure involved in the production of disc wheels is large; but the output also is large, and, as the volume increases, the prices become lower. The difference in the cost of painting is another item in favor of the disc wheel over both its competitors, even when the same number of coats are applied, but if high-bake enamel is used a surprising saving can be effected.
Two objections at first arose because of its demountable features: the first, because special carriers were required when the demountable-at-hub type was used; the second, because the demountable-at-rim type made it necessary to get under the car to adjust the brakes. Local conditions produce differences of opinion, wood and wire wheels being preferred in certain sections during wet periods because of the greater facility of handling the wheels by taking hold of the spokes. One of the most serious objections has been due to the trouble experienced in inflating the tires. Efforts to conform to the standards of other wheels brought complications in the use of the valves, so that it has become evident that, to secure the best results, steel wheels must be built around standards of their own.
It is possible to design a disc wheel with a lateral resiliency greater than that of any other type. This is particularly noticeable in turning corners, as it affords material relief to the tires. The tapering of the disc wheel toward the rim causes it to take a deflection readily at the rim but resists it in an increasing ratio as the deflection increases; it thus withstands impacts such as those against a curb that would cause a wood wheel to crack. Much must yet be done with the design to bring disc wheels into common usage, the features that require special study from a technical standpoint being strength, resiliency, fatigue, weight, noise and appearance. An advantage in weight formerly lay in favor of the wood wheel but this condition no longer exists, the disc wheel weighing slightly less in the 32 x 4 in. and the larger sizes. The difference in the energy consumed in accelerating the wood and the disc wheels has been found to be less than 0.01 per cent, which is less than the loss of energy due to windage in accelerating a non-skid tire as compared with that of a smooth tire under the same conditions. Reverse curves and crimps in the disc not only increase the rigidity but tend to restrict the amplification of sound vibrations. The difficulties attendant upon the securing of steel of sufficient and uniform hardness seem to have found solutions in the heat-treating of the metal before or after drawing, or in the using of carbon-steel drawn hot and hardened in a die afterward. Both involve manufacturing difficulties but give a uniform product, and increased strength and a reduced weight.


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