holes in the tire. Repairs to solid tires can best be made at the factory where they are produced and these are seldom necessary unless the tire has been cut by accident. As a rule when a solid tire wears down the only practical remedy is to replace it, as it is not susceptible to retarding as the pneumatic tires are.

Modern Tires Are Well Made.-There is an impression obtaining with motorists, and even with many engaged in the industry, that tire expense is an element in automobile maintenance depending more upon good fortune than any care of the tire manufacturers in producing good tires, or in the motorists using reasonable judgment and care in driving, and taking precautions that the shoes will receive the same attention given other components in the vehicle. The average person, whether tradesman or layman, seldom considers the enormous stresses to which tires are subjected on even the lightest of runabouts and motorcycles, and as a general rule after shoes are fitted to the rims, they are forgotten until abuse or careless driving causes sudden end to their usefulness. Natural wear may make replacement necessary and while the American manufacturers of tires are producing types that are enduring and practical, with even the best of care the tire must eventually wear out. Some standard tires may be better than others, but all are good and will give satisfactory service if properly used. The fact that the efficient motor car of to-day would not be possible or practical without the resilient support and increased tractive effort given by the pneumatic tire is not often considered, and tires are regarded as a necessary evil, though they are really one of the most essential and hardest worked components of the motor vehicle.

It is not intended to go into the details of tire manufacture, or to compare one form with another, as the actual methods of construction are of little concern to automobilists and those in the trade; and instead of a review of the technics of tire manufacture, the writer desires to give some practical information relative to the processes of repairing tires found to be satisfactory in application, based on experience gained in both factory and shop. Such detail is seldom published and many motorists and repairmen assume that automobile tire repairing is a mysterious occupation that is beyond their comprehension. Not only among automobilists, but

throughout the greater portion of the trade as well there is no very clear conception of the processes or the careful manipulation necessary to repair tires successfully.

1

Construction of Tires.-While much advice has been given relative to the care of tires it will be well to speak of some causes of deterioration, and for the better knowledge of the uninformed reader the conventional methods of tire making and the qualities of the materials used are outlined. The principal materials in vehicle tires are rubber compounds and textile fabrics, and every factory has its own peculiar processes of combining these to form the finished tire. Practically all tire manufacturers procure the fabric from firms making a specialty of textile products, but generally any concern manufacturing rubber goods prefers to use those special compounds which experience has shown are best adapted for the appliances they manufacture. The basis of all tires is undeniably fabric and crude rubber, both of which are of vege table derivation, the best fabric being of Sea Island cotton, while the caoutchouc, or India rubber, is the product of a great variety of trees, vines and shrubs, most of which grow in the torrid zone.

The substance which gives the modern tire its strength is the fabric forming a basis for attachment of the rubber, and while many materials have been tried, among them silk, wool and linen, cotton alone combines most of the required qualities. Before incorporation in tires this fabric is thoroughly dried and impregnated with rubber. Nearly all tires are formed or built on cores and are composed of layers of fabric and rubber.

At Fig. 422, A, a sectional view of a "bolted-on tire" is shown which will serve to illustrate the manner in which a tire is built of layers of materials. The outer layer is specially tough rubber known as the tread, of such composition it is strong and specially adapted to resist abrasion, firmly attached to two layers of fabric, known as breaker strips, which rest on another layer of softer and more resilient rubber than that of which the tread is composed. termed the cushion or padding. The main body of the tire consists of layers of the frictioned or rubber impregnated fabric, the number of plies varying with the size of the shoe. In the base of the tire are incorporated hard rubber and fabric fillers to make the

structure of maximum strength. These successive layers are then put into intimate relation by vulcanization.

Cause of Deterioration.-It is evident the pneumatic tire is a combination of materials that in themselves are not specially enduring, and it is not reasonable for one to expect lengthy service from a tire. In considering the causes of deterioration we will assume the tire is a standard product of a reputable maker whose processes of manufacture eliminate defects which might result from poor material or workmanship. If the shoe is poorly made it will heat and the layers of fabric and rubber will separate, or the side walls will crack; if the wall is too thin or of insufficient strength it will blow out, tear or cut, and at the other hand if there be too much fabric used and the walls are too thick, the flexibility is reduced, the difficulty of bending under load is increased, the side walls are forced to assume sharp angles and the fabrics will be ruptured. If the tire be not properly vulcanized, the layers will loosen from each other and if the rubber compound is not right deterioration will be rapid. If the tire is cured too long its life. will be short, because the process has changed the chemical composition and physical characteristics of the materials employed. It will be evident that if one regards only the product of experienced makers that faults due to poor construction and material cannot be logically considered.

Perhaps the most common cause of tire deterioration is abuse by the user, and on the other hand there are unavoidable causes, such as punctures or hard service. Overloading and insufficient inflation are the two most common causes of poor tire service, and it is seldom that the motorist observes the most simple requirements that will insure satisfactory tire life. Each size of tire is designed by its makers to carry a certain weight which should never be exceeded, and if the weight schedule is followed in designing or equipping a car, good results may always be expected from tires, provided they are not otherwise abused. If the shoes are overloaded reasonable service cannot be expected, as no tire, no matter how well made, can continually resist the internal pressure necessary to keep it inflated enough to support the load when of insufficient capacity.

The most important advice given the purchaser of tires is to keep them properly inflated, and its value cannot be overestimated. More tires become useless from use with too little air pressure than all other causes combined, and while most drivers assume they have sufficient air in the tires they use it is a fact they habitually use tires that are not properly filled. The tire should contain air enough so that it shows but little change in form when the car is standing on a hard surface under full load, and even under these conditions it will be found that the tire is compressed considerably when the car is in action.

The Cord Tire.-A method of tire construction that is becoming popular because of its easy riding qualities is a difficult form to repair and is shown at Fig. 420. Instead of layers of fabric the main portion of the carcass, or casing, is composed of cores which are passed around small wires at the base of the tire and which are wound very tightly in order to secure intimate contact between the various layers of cord. Sheet rubber is placed between the cord layers and fabric breaker strips are placed between the tread and the cord body in the usual manner. When the tire is vulcanized the spaces between the layers of cord become filled with the rubber, and the whole mass is firmly bound together. The wires project into the bead portion of the tire and are vulcanized firmly in place. Owing to the construction a cord tire cannot be as easily repaired as the fabric type because it requires a very expert knowledge of cord tire construction to replace injured portions due to a blowout. As we shall see, the fabric tire may be restored to efficiency by cutting out layers of the defective fabric and vulcanizing new layers in their place. This is not a difficult operation, whereas replacing the defective cords calls for a degree of skill not usually possessed by the tire repairman.

Rims for Pneumatic Tires. An expert has stated that there are at least forty different types of tire retaining rims that have received general application and that these require at least fourteen different sections of wood wheel felloes. Besides the various well known and popular rims a number have been designed that are more or less complicated and which are said to possess various desirable features by their manufacturers. There are six repre

Fig. 418.-Standard Clincher Tire and Rim Dimensions.

sentative groups into which the various rims manufactured to-day may be classified. These are: 1. One piece clincher. 2. Quick detachable clincher. 3. Quick detachable straight side. 4. Quick detachable universal. 5. Demountable. 6. Demountable detachable. The distinction between the two last classes is that there are a large number of demountable rims which have to be taken off of the wheel before the tire can be removed. There are others that not only have the demountable feature but from which the tire can be removed while the rim remains on the wheel.