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Width of Tires

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The effect of the width of wheel tires upon the resistance to traction has already been mentioned in Art. 2. For ordinary roads, not in soft condition, tractive resistance is somewhat less for wide than for narrow tires. This difference, while not usually very great, is sufficient to be quite appreciable in the work of hauling heavy loads upon the roads. Narrow tires have a much more destructive effect upon a road surface than wide ones, and from the point of view of road maintenance, wide tires are very desirable. The concentration of a heavy load upon narrow wheel tires affords very little surface of contact between the wheel and road, and causes the wheel to indent the road surface, giving a powerful cutting action. The same load on a tire of sufficient width would tend to compact the ` road, acting like a roller, and if these wheels are so placed as not to run in the same track, the difference would be still more marked. There is, however, no advantage in an excessive width of tire. When this exceeds 4 or 5 inches, upon a properly crowned road, the tire will be only partially in contact with the road and the load will be carried on one edge of the tire, which will indent the road surface.

The general introduction of wide tires upon vehicles traveling our highways would greatly simplify the problem of road maintenance, particularly upon earth roads. This fact is generally admitted and appre

ciated by road builders, but the practical difficulties met in attempting to change the prevailing system of narrow tires has been too great, and the agitation for wide tires has not as yet produced much effect. Many propositions have been made looking toward the regulation of the width of tires by law. This has not met with much success. In some states the laws provide for a rebate upon road taxes to persons using wide tires upon wagon wheels used for highway transportation.

The usual width of tire upon ordinary wagons is i or it inches. For the best effect upon the high ways, these should be increased so as to vary from about 3 to 5 or 6 inches, according to the load for which the wagon is designed.

The wide tire is at a disadvantage on a distinctly bad road, and efforts to secure the adoption of wider tires can hardly meet with much success until very great improvement has taken place in the character of the country roads. Wider tires should- naturally follow better roads and assist in maintaining them.