RUBBER TIRES. The earliest mention of rubber tires in literature is contained in a work by Thomas Hancock published in 1856, in which he suggests the use of rubber tires on vehicles for the purpose of avoiding vibra tion. Prior to this, however, a patent for an elastic tire had been granted to Robert William Thompson in 1845, and it has been frequently suggested that this patent anticipated the pneu matic Dunlop tire. As a matter of fact, it appears to have been satisfactorily proved that Dunlop's invention was developed quite inde pendently of any knowledge of Thompson's work. Thompson's tire consisted of an elas tic belt made of a number of folds of canvas saturated and covered on both sides with rub ber or gutta-percha in a state of solution. The inner tube so obtained was to be protected by a cover built up around the tire, made by rivet ing together circular segments of leather and bolting these to the tire. There was also provision by means of a pipe passing *through the tire* for inflating with air. As far as can be ascertained, very little practical use was made of Thompson's invention. In 1856 a solid tire composed of cloth or other fibrous material and rubber sheet in alternate layers was made by W. Coles Fuller. This tire was made up on a cylinder fastened to the wheels by means of flanges. The introduction of the bicycle about 1869 gave the necessary impetus for the further development of the solid tire and sub sequently of the pneumatic type. In 1888 the pneumatic tire as we know it was invented by Dunlop and at once came into universal use on the bicycle. In England and on the Con tinent, an outer casing containing an inner inflated tube was attached to the wheel-rim, while in America a single tube cemented to the rim was more generally used and to this day holds its place on The bicycle. With the advent of the automobile a new field opened for the pneumatic rubber tire. The simplest form of automobile tire is a solid band of rubber, next come the several forms of cushion tires in which the band of rubber is perforated with a number of small holes or provided with a series of openings with the object of obtaining greater resiliency and of making the tire more yielding than the solid rubber type. Solid tires are to-day practically confined to commercial and industrial vehicles, such as delivery trucks, wagons, etc. The great weight and speed of passenger automobiles and their delicate con struction require additional protection from vibration to that furnished by springs alone. The -pneumatic tire is now in general use on such vehicles, for with these tires the car is suspended in air, which is the most elastic of substances. The most common form of tire is composed of a hollow rubber tube of circu lar section filled with air and protected from wear by means of an outer shoe or casing. The inner member or tube is made of a very pure rubber, about one-eighth inch thick for cars of average weight. While this tube is very elastic and is air-tight, it would not be strong enough or have adequate resistance to be run directly in contact with the road surface, there fore, it is necessary to protect it by a shoe composed of layers of fabric and rubber coin position. The shoe member is provided with beads on its inner periphery designed to inter lock with the rim channel. A steel rim is
placed around the felloes of the wheel and shaped to fit the shoe or casing, its exact shape depending on the design of the tire. The part of the shoe which comes in contract with the road surface is called the tread. The main part of the shoe or casing is made up of five or more layers of a Sea Island cotton fabric *frictioned* with high-grade rubber composi tion. This is forced into the mesh of the cloth by machinery so the fabric will be prac tically waterproof and will join intimately with the other plies by a process of vulcanization when the shoe is cured. Outside of the fabric body a layer of very resilient rubber, approxi mately of crescent form, known as the padding, is provided to give elasticity to the shoe. Between this member and the tread a number of pieces of heavy fabric called ((breaker strips* are interposed to offer a certain degree of resist ance to any sharp object penetrate the tread and go through the *rig and into the fabric body, The tread is the tire part subjected to the greatest stress, as it mist resist the abrading influence of the road, and., in the ease of the rear tires, the wearing effect of the friction of the tractive effort. The tread, accordingly, is of very tough robber com position and does not possess a very great de gree of elasticity, which is here sacrifted for strene and reststance to wear. Air is pumped into tire through a form of automatic valve, firmly attached to the inner tube and projecting through the steel rim and felloe. The valve is held in its seat by a tension spring, and opens only when the pressure of the incoming air is greater than the pressure within the tube. Tires are sometimes classified according as they have a smooth tread or a non-skid tread. The non-skid type has. a roughened surface, either small cups, knobs, steel rivets, etc., do. signed to prevent skidding on slippery high ways, Chains are also used for the same per pose, being so made that they are quickly at tached or detached, as the necessity arise!. Their form is too well known to requite description. The casing or shoe of automo bile tires differs also in the manner of their seating or attachment to the rim. The clincher type is perhaps the most popular and simplest in that the shoe is held against the rim when the tube is inflated. Another form is known as the demountable. All these varieties have in view to facilitate a more ready removal from the wheel or to make for a more secure attachment The quick detachable rim is the more modern type. It is permanently fastened to the felloe of the wheel, but the outer clinch of the rim is removable, permitting the casing to be easily pulled off. American tire manu facturers have adopted the following propor tions between axle loads and tire sizes : 2t.inch tires, all diameters 225 pounds per wheel 3 tech tires, all diameters 350 31 x 28 3 x 30 450 " 3 32 II * 3 34 600 * 3 36 600 U & 4 x 32 650 ft Id 4 x34 700 " " 4 x36 730 If IS 4e x 34 800 " " 41 x36 900 The air pressures for inflating pneumatic tires recommended by the same authorities are as follows: Diameter of tire, Maximum weight Air pressure is inches on wheel. lbs. tire, lbs. pr. eq. in.