Fig. 230.-Standard American Anti-Skid Treads of Various Designs Showing Methods of Obtaining
Rough Treads.

Q. What is the advantage of a smooth tread tire and under what conditions is it inadequate?

A. Smooth tread tires are simpler to make and cheaper to buy than the various anti-skid tread types and are the most suitable for general use on dry, hard roads. They have superior adhesion and the tread will wear much more uniformly than do "rough tread" tires. One disadvantage of the smooth tread casing is that it will not provide sufficient traction on slippery roads and a car is apt to skid more under these conditions than if it is provided with rougher or irregular tread tires which have a better grip on soft roads.

Q. What are features of various "rough tread" tires?

A. The most important feature gained by the use of rough treads is the elimination of a large degree of skidding and more positive traction under certain conditions of operation. The leading types of anti-skid tires are outlined at Fig. 230 and it will be apparent that there are many ways of obtaining the desired end. For the most part, various irregularly shaped projections or studs of rubber compound are moulded on the tread, these varying from simple round buttons or elongated bars to more complex forms composed of stars or imitating basket-weave or chains and one maker even goes so far as to mould a series of letters on the tread which imprints the words "Non-Skid" in mud or other such yielding road material. The most practical forms are those in which the projections are of sufficient size to prevent rapid wear.

Q. What is the inner tube, and of what material is it made? A. The inner tube or air bag of the tire is composed almost entirely of pure Para rubber having only enough sulphur in the composition to insure the proper degree of curing. The inner tube is very elastic and is air tight and can be inflated to several times its normal diameter without danger of rupture. It is not suitable to resist wear as the resilient rubber of which it is composed would soon be destroyed if it came in contact with the road surface so it is protected by the more strongly constructed casing or shoe.

Q. What prevents chafing between inner and outer tire members?

A. As the inner tube is fully inflated, it entirely fills the space inside of the outer casing and there can be but little relative movement. In order to prevent chafing it is customary to use talcum powder as a lubricant to prevent friction between inner and outer members.

Q.

What are tire lugs and where are they used?

A. When clincher tires are applied to heavy cars capable of high speeds it is customary to supplement the natural wedging action of the fully inflated inner tube forcing the tire beads in the rim channels by means of security bolts. These have an approximately Y-shape and are depended on to force the bead firmly into the rim channel at four or six points on the wheel periphery. The shank portion of the security member is a threaded bolt passing through the wheel rim and felloe and screwed in place by a wing nut. The head portion of the security member is V shape, composed of rubber or fabric built around a central metal core of sufficient size to bridge the gap between the two beads and hold them firmly into the channel. At the present time quick detachable tires are given preference and tire lugs are seldom used because the lighter cars using clincher tires do not need them.

Q. What is the life of outer casings?

A. The amount of service received from an outer casing, assuming that it is made of proper material and cured in a careful manner, depends upon many conditions, some of which are under the direct control of the operator, while others are unavoidable. The factors of car weight and speed are important and casings invariably last longer on light, moderate speed cars than they do on heavy high speed vehicles. On heavy touring cars a casing that receives average attention is considered to have rendered satisfactory service if the tread will not wear down to the fabric until 2,000 to 3,000 miles have been covered. On lighter cars casings have been known to run from 5,000 to 6,000 miles without becoming weakened sufficiently to require removal.

Q. What precaution must be taken to secure proper mileage? A. Tire makers all recommend that the tires be examined carefully from time to time in order to observe a few simple rules. The

casings should be looked over to see if there are any serious cuts or bruises penetrating to the fabric and allowing water to find its way into the textile material and cause it to rot. The tires should also be properly inflated as it is claimed that fully 75% of all tire troubles outside of those due to natural depreciation are caused by insufficient inflation and overloading of tires.

Q. What are the best tire sizes for various vehicle weights? A. Each size of tire is designed to carry a specified weight and as many times cars are equipped with tires which are barely up to the requirements, the following table recommended by the U. S. Tire Company will act as a guide to enable the motorist to see if the proper size of tire has been provided by the car manufacturer. The cars are to be weighed without passengers or luggage and each end of the car is to be weighed independently of the other. This is done by selecting a point on the frame midway between the two axles, and marking it in some way so that it can be easily distinguished. The front end of the car is then run on the usual form of heavy platform coal or hay scale, until the mark indicating the central position is just over the edge of the scale. This weight gives the approximate amount to be carried by the two front wheels. The car is then reversed and run over the scales until the rear parts rest on the platform. This weight as indicated on the scale beam shows the amount of load carried by the two rear wheels. The entire car is then placed on the platform and the total weight taken to see how it checks up with the sum of the two previous readings, which thus provides an approximately accurate check on the correctness of the first trial.

and inflation

Q. Is there any relation between tire size pressure?

A. There is a very definite relation between the amount of air pressure for the various sizes of tires. As a rule, the larger tires which are heavier in construction and are depended on to carry the greater weight must be blown up to a greater degree than the smaller