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TIRE

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Originally appearing in Volume V26, Page 1009 of the 1911 Encyclopedia Britannica.
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TIRE , an homonymous word, of which the meanings are (1) to weary out, (2) to adorn, or, as a substantive, a See also:

head-See also:dress, (3) the See also:outer rim of a See also:wheel. " Tire " in sense (I) is from the Old See also:English tcorian, to weary, transitive and intransitive. Ultimately this word is connected with" See also:tear," to rend, the stages of meaning being to rend apart, to See also:wear out, to be or make exhausted. In sense (2) the word is a shortened See also:form of " attire," dress, equipment; this is from the Old See also:French atirer, to put in See also:order, tire, a See also:row, hence the word now spelled in English tier, but earlier found as tire or See also:tyre. " Tire " (3) is somewhat obscure etymologically. It may be connected with " attire," especially with reference to a similarity to the See also:band of a woman's head-dress, or it may be a corruption of " tie-r," meaning that which " ties " or fastens together, though this is rejected by See also:Skeat. The spelling " tyre " is not now accepted by the best English authorities, and is unrecognized in See also:America. The tire of a wheel is the outer circumferential portion that rolls on the ground or the track prepared for it. When the track is smooth and level, as in a railway, the See also:principal functions of the tire are to provide a hard, durable See also:surface for the wheel, and to reduce to a minimum the resistance to See also:rolling. Railway vehicle wheels usually have hard See also:steel tires, this See also:combination with the hard steel See also:rail giving the maximum endurance and the minimum rolling resistance. For road vehicles also, in which durability is the See also:prime See also:consideration, the tires are usually rings of See also:iron or steel shrunk on the wooden wheels. In bicycles, motor-cars, and other road vehicles in which freedom from vibration and See also:shock from uneven road surface is desired, See also:rubber or pneumatic tires are employed.

These elastic tires are capable of absorbing small irregularities in the road surface without transmitting much vibration to the See also:

frame of the vehicle. Their range of yield is, however, too limited to absorb the larger irregularities met with on rough roads, so that their use does not obviate the See also:necessity of See also:spring support of the See also:carriage See also:body on the wheel axles. The pneumatic tire has a very much smaller rolling resistance than a solid rubber tire. Where the See also:driving See also:power is limited, as in bicycles, this consideration is by far; the most important. A pneumatic tired See also:bicycle requires less power to drive it at a given See also:speed than does one with solid rubber tires—in popular See also:language, it is much faster; hence pneumatic tires are now almost universally used on bicycles. Rolling Resistance.—See also:Professor See also:Osborne See also:Reynolds, in his investi- gations on the nature of rolling resistance, found that it is due to actual sliding of the surfaces in See also:con- tact. Fig. I shows an iron See also:roller resting on a See also:flat, thick See also:sheet of See also:india-rubber. A See also:series of equidis- tant parallel lines See also:drawn on the india-rubber are distorted by the The distance between the marks on the periphery of the roller corresponds to that between the lines on the undistorted sheet of rubber. The See also:motion of the roller being from See also:left to right, actual contact takes See also:place between C and D. The surface of the rubber is depressed at P, is bulged up in front at D, and behind at C. The See also:vertical See also:compression of the rubber at P causes it to bulge laterally, this causing a lateral contraction at D, which in turn causes a vertical See also:extension at D.

There is thus created a tendency to relative creeping motion between the roller and rubber. Between f and e there is no relative sliding, but over the portions eD and Cf there is slipping, with a consequent See also:

expenditure of See also:energy. The See also:action causes the actual distance traversed by the roller to be different from the geometric distance calculated from the See also:diameter and number of revolutions of the roller. A certain amount of energy is expended in distorting the rubber between P and D; See also:part of this energy is restored as the See also:rear portion of the roller passes over this and the rubber gets back to its See also:original unstrained See also:state. With a solid rubber tire rolling on a hard, smooth surface the action is similar. Fig. 2 shows a portion of the tire flattened out: --~ pi and p2 are the intensities of the pressures at points al and See also:a2 at equal distances in front of and behind c, the geometrical point of contact: pi opposes, p2 assists the rolling of the wheel. At usual speeds the opposing force, pi, will be greater than the force of restitution, p2, the difference being a measure of the elastic See also:hysteresis of the material, H, at that speed. If the vertical compression cd of the tire be denoted by y, the energy lost may be said to be proportional to Hy. Comparing three tires of steel, solid rubber and See also:air respectively rolling on a smooth, hard surface, H is probably smallest for steel and largest for rubber, y is least for steel, greater See also:fee a pneumatic tire pumped 1007 hard, greater still for solid rubber and for a pneumatic tire in-sufficiently inflated. The rolling resistance of the steel tire will therefore be least; next in order come the pneumatic tire inflated hard,'and the pneumatic tire inflated soft, while the solid rubber tire has the greatest resistance. Pneumatic Tires.

See also:

Weight Supported.—Let a pneumatic tire inflated to p lb per square See also:inch support a load W lb. The portion 441= near the ground is flattened (fig. 3). If the tire fabric is assumed to be perfectly flexible, then, since the part in contact with the ground is quite flat, the pressure p and q on the opposite sides must be equal; that is, the tire presses on the ground with an intensity p lb per square inch. The See also:area of the flattened portion is therefore W/p. Fig. 4 shows the'7shapes of the areas of contact of a bicycle tire 28 in. by If, in., for various amounts of vertical flattening, the figures annexed to the curves in See also:plan and to the corresponding lines in See also:elevation indicating the amount of vertical flattening in sixteenth parts of an inch. Let y be the vertical flattening, a the semi-See also:major See also:axis, and b the semi-See also:minor axis of the See also:curve of contact. For small values of y, corresponding to a tire pumped hard, the curves of contact may be considered See also:plane sections of a circular See also:ring. The area of the curve may be taken equal to that of an See also:ellipse having the same axes, i.e. ,See also:rab. But a=slR2—(R—y)2=s/2Ry—y2= dy sl 2R—y, and b=VIr2—(r—y)2=Jy 112r —Y , R and r being the principal radii of See also:section of the tire longitudinally and transversely.

Therefore, approximately, A=vrab=ay 12R—y,l2r—y For small values of y, y may be neglected in comparison with 2R and 2r respectively, and the above See also:

equation becomes A = 2irysl Rr = iryiiDd, and therefore W=2irypsiRr=aypJ/Dd. For larger values of y, A is smaller than that given by the above See also:formula, as shown in fig. 5, which gives the areas of contact plotted with respect to the vertical flattenings for a tire 28 in. by si in. The same curve may serve to show values of W, thus corresponding to the load-deflection curve of a spring. The curve clearly shows the small value of the pneumatic tire as a spring See also:device. Thus, when pumped hard, so that the normal load is carried with e in. vertical flattening, when , the bicycle is travelling quickly, a lump on vrd niftare,,;~ xi°. the road See also:equivalent toe in. further flattening FIG. S, nearly doubles the upward reaction on the wheel. With the normal load carried with s in. vertical flattening the same lump on the road increases the upward reaction by only 23 %, the area of contact of the tire being ;b c, ..ss--s ;b '•,d increased from 6.5 to 8 sq. in. The above brief investigation, involving a few approximations, is yet sufficiently accurate to afford a clear See also:idea of the usual conditions of a tire. io Outer See also:Cover.—The outer cover has to be strong enough to with- stand the air-pressure inside the tire and to transmit the driving or the braking effort from the wheel to the road surface. For the latter purpose, the threads of the fabric are best disposed spirally, as shown in fig. 6.

While driving in the direction of the arrow the tension on the See also:

fibres cc will be slightly increased, that on fibres dd decreased. The distortion of the fabric due to driving is thus reduced to a minimum. A See also:woven fabric is sometimes used, but one made up of two or more layers of parallel threads embedded in rubber is better. This construction makes the outer cover more flexible, and consequently less energy is wasted in distorting the fabric as the tire rolls on and off the ground, while greater durability is also secured. Fig. 7 shows a See also:plain woven e v. ®~ rsra fabric, from which it is seen that each See also:thread takes the form of a sinuous See also:line. As the air-pressure inside the tire is increased the threads tend to become straighter, thus pressing together with a cutting action. The See also:total thickness is greater than that of two layers of parallel threads, while on the latter the threads can be placed closer together. The woven fabric is therefore stiffer, weaker and less durable than that built up of parallel layers. The See also:average See also:longitudinal section of the cover is given by the formula pd=2ti; that on the transverse section, t2, by pd=4t2, d being the diameter of the tire in transverse section; consequently the stress on the longitudinal section is twice that on the transverse. With the See also:spiral disposition of the threads, as shown in fig.

6, this inequality of stress in the two principal directions has the effect of tending to enlarge the transverse section of the tire, while at the same See also:

time tending to See also:contract the tire on the rim. Single See also:tube, See also:Double tube and Tubeless Tires.—A tire, beside being strong enough to resist the stresses to which it is subjected, must be air-tight. In most tires for cycles and motor-cars an inner tube of india-rubber is made See also:separate from the outer cover. In these double-tube tires the outer cover is more or less easily detachable from the rim. The air under pressure is pumped inside the inner tube, which is sup-ported by the outer cover. In See also:case of puncture of a bicycle tire, the inner tube is repaired by cementing a patch of rubber on the outside of the inner tube, a See also:solution of india-rubber in See also:naphtha or bisulphide of See also:carbon being the cementing See also:agent employed. Motor-See also:car tires are best re-paired by vulcanizing, as solution patches usually come loose owing to the See also:heating of the tire. In a single-tube tire, as its name indicates, the outer cover and the air-tight tube are vulcanized together to form a single hollow ring. To repair a See also:simple puncture of a single-tube tire it is not necessary to detach it from the rim. Single-tube tires are not often used now, except for path-racing bicycles. A tubeless tire, such as the " Fleuss " (fig. 8), consists of the outer cover, as used in a double-tube tire, to the inner surface of which an air-tight layer of sheet-rubber has been cemented.

A continuous flap projects from one edge of the tire, and when in position on the rim this flap is pressed against the other edge, forming an air-tight See also:

seal. A slight moistening of the flap with soft See also:soap tends to remove any imperfection in the tightness of the air seal. The repair of a puncture of a tubeless tire can be very quickly done. Since the inner surface of the air-tight layer is accessible, after placing the patch in position the tire can be inflated and the bicycle ridden at once; whereas in the double-tube tire sufficient time must elapse between the patching and the inflation to allow the rubber solution to set. See also:Attachment of Tires to Rims.—A single-tube tire can be cemented `directly to the rim. For detachable double-tube tires on bicycles, two methods, the See also:Dunlop-Welch endless See also:wire (fig. 9) and the " beaded edge " (fig. II), See also:account for by far the greater proportion. In the Dunlop-Welch tire the endless wires are embedded in the two edges of the outer cover respectively, the transverse tension of the fabric being transmitted to them. Each endless wire is formed of three coils, oUNLOG.— so as to give flexibility to the edge of the .WELCH fli cover. The ring formed by each endless between T and Q. Then for each inch length of wire T=pd/2, Q=T/See also:cos 0; while P=QD/2.

Combining these results, we get P=pdD/4 cos 0. If 0 =30`, P=o•29pdD, from which the section of wire for a tire of any See also:

size can be calculated. In the " beaded edge " fastening, thickened edges on the outer cover take into corresponding edges formed on the rim, and are securely held therein when the tire is inflated. Prevention of Punctures.—The outside of the tire is covered with a thick layer of rubber, which protects the fabric from injury by contact with the rough road surfaces. In full roadster tires this outer layer of rubber is thinner at the sides than at the tread (the part which actually rolls on the ground), but still completely covers the fabric. In See also:light roadster and racing tires the sides are not covered, and an appreciable gain in speed or ease of driving is due to the greater flexibility of the cover thus obtained. Numerous puncture-See also:proof bands and other devices have been tried with the See also:object of absolutely preventing punctures, or making the tire self-sealing after puncture; but they increase the rolling resistance, and therefore the effort necessary to drive the bicycle at a given speed. See also:Valve for Pneumatic Tire.—A non-return valve is permanently attached to the inner tube of the tire, which allows the air forced from the inflater to pass inside the inner tube. The most commonly used, the Dunlop-See also:Woods valve, consists of a See also:short piece of rubber tubing mounted on a See also:brass See also:stem, which has a small hole communicating from its outer end to the inner surface of the rubber tube. Normally, the tubing closes the mouth of this hole, preventing the air from escaping from the tire, but lifts freely when air is being forced from the inflater. The arrangement of the parts for deflating and for getting See also:access to the rubber tubing is very simple and effective. The cyclist should be careful that the small piece of valve tubing, and the two fibre washers at the ends of the flexible connecter which serve to make air-tight the two See also:joints between the latter and the See also:pump and valve stem respectively, are always in See also:good See also:condition.

If either of these seemingly small details is out of order it may be impossible to pump the tires hard enough; the bicycle being ridden, the tires may be nipped in many places between the rim and See also:

sharp edges on the road surface, and practically ruined. Tires for Motor Cars.—In the cost of upkeep of a motor car the tires are the most expensive See also:item. For a slow speed vehicle an See also:ordinary steel tire, shrunk or hydraulically pressed on a wooden wheel, Is cheap and durable. At higher speeds over uneven roads it is less satisfactory; the wheel, forming with the tire one rigid body, receives violent accelerations vertically, due to the uneven road, and is being continually shot upwards into the air out of contact with the ground. Thus excessive See also:noise and vibration are caused at all but very moderate speeds, and for passenger cars an elastic tire is a necessity. The solid rubber tire, not being liable to puncture, is trustworthy if made of sufficient sectional area, but it is expensive and lacks the comfort and easy See also:running of the pneumatic. The motor car pneumatic tire is made on the same lines as the See also:cycle tire, but the air-tube is thicker, and the outer cover is built up with several layers of See also:canvas or fabric to give the necessary strength (fig. 14). To provide for wear, the outer protective layer of rubber is considerably thickened at the tread, where it is also reinforced with two or three layers of canvas. The See also:Palmer See also:cord tire is built up of two layers of cord (fig. 12) arranged spirally, each cord being composed of four strands of six threads. The cords are flattenec tire, and their wide ones at the beaded edge.

The anchorage of the cord to the beaded edge is obtained by steel pins passing through the loops of the cord and into the canvas beads (fig. 13). The cords, tread and beads being all vulcanized together, the tire is practically impervious to moisture, and has there- fore less tendency to rot than a canvas tire. See also:

Fur- ther, the threads, by the See also:process of manufacture, are insulated each from the others by a layer of rubber, and there is thus less tendency for them to fray or saw each other as the tire yields dur- See also:ing continuous running. These features of con- durability. Strains on Fabric of Pneumatic Tire.—As each portion of the tread comes in contact with the ground it is flattened, while the See also:rest of the transverse section has its See also:radius of curvature slightly decreased (fig. 3). Thus the transverse section is repeatedly undergoing flexure through a range extending from flatness (radius of curvature infinity) to a radius of curvature slightly less than that of the normal section. On the longitudinal section the range of flexure is from flat to a radius of curvature equal to that of the normal section. The latter range is therefore much less than the former. The necessary thickness of the fabric and rubber to resist the air pressure and punctures involves a certain amount of stiffness; consequently the energy expended in the flexure of the tire is much greater than in a thin cycle tire. This energy appears as See also:heat; the temperature of the cover rises until the heat carried away by the air is equal to that generated by flexure.

At very high speeds this heating becomes so See also:

great as to have an injurious action on the rubber and fabric. Unfortunately, the solid rubber tire is worse off in this respect, its elastic hysteresis, and there-fore the heating effect, being greater than that of a pneumatic tire. It is evident that increase of the diameter of the tire-section lessens the heating action, while reduction of diameter of the wheel has no effect, so See also:long as the range of longitudinal flexure is less than the transverse. Nearly all tire fabrics are equally stiff longitudinally and transversely; but probably greater durability would be obtained from a fabric more flexible transversely, even if somewhat stiffer longitudinally. Pneumatic Tires for Heavy Loads.—From the formula for load supported, W=iryp~D, for a given air pressure p and vertical flattening y, the load supported is proportional to the square See also:root of the product of the longitudinal and transverse diameters; thus a tire 36"X4" is equivalent to one 24"X6". But the latter can be subjected to a much greater vertical flattening y than the former, with a less range of flexure of the cover, probably twice the amount. In this event, with the same air pressures, the 24"X6" tire could carry a load twice that of the 36" X4" tire. Or, if both tires carried the same load, the air pressure in the former might be See also:half that in the latter, and, its vertical flattening under normal load being twice as great, its value as a spring in absorbing vertical unevenness of the road would be double. Since the first use of pneumatic tires for motor cars, they have been steadily reduced in diameter, and probably they can be made still smaller with See also:advantage, if the transverse section be proportionately increased. The following table gives the maximum loads and minimum air pressures for a few sizes of tires, as recommended by the Dunlop Pneumatic Tire See also:Company. The corresponding vertical flattening has been calculated from the formula given above. Diameter.

Section. Maximum M Minimum Vertical Load per Air Flattening. Wheel. Pressure. Light In. In. lb lb In. 28 2a 36o per sq. in. •19 70 Car 28 3 400 75 .19 Tires 28 3a 700 8o .25 Heavy ( 32 3 is 900 8o 33 Car jl 32 4 1000 85 •33 Tires 32 5 1300 95 •34 (fig. 14). Fig. 13 shows a flange fastening as used for the Palmer cord tire, the two flanges being secured by a number of bolts passing through the rim of the wheel. Solid Rubber Tires for Heavy Vehicles: Fig.

15 shows a section of a solid rubber tire and rim, the rubber being forced under pressure on the beaded rim. For very heavy loads, as in motor omnibuses, a twin tire gives the best results. The two tires are fastened on the same rim, at a sufficient distance apart to allow each to bulge laterally as it rolls on the ground. Non-Skid Devices.—As a pneumatic tire flattens where it is in contact with the road, under certain conditions of road surface a semi-liquid film of mud gets interposed, and frictional contact is reduced to a minimum. The vehicle has then no Iateral constraint, and See also:

side-slipping or skidding may occur. Ong a bicycle this means a dismount, probably a See also:ooh severe fall; on a three or four-wheeled i' co vehicle the steering See also:control is temporarily 000 lost. Cycle tires are usually provided with g i ;goo . longitudinal ridges at the tread (See also:figs. 8, 9, 1 i) ; the narrow surfaces of the ridges penetrate the mud and get a better grip on the solid road surface. Motor car tires are sometimes left with a smooth tread (fig. 14); fig. 13 ~i I;,~(i•,y shows a non-slipping tread with longitudinal ~~"" ridges. The Dunlop non-slipping tread is ~~~ ;~•,~: formed by a series of lateral grooves about 2 in. apart all See also:round the tread.

Fig. 16 shows a tire fitted with a non-skid See also:

leather band, to which hard steel studs are fastened. This of to non-skid the ki band o tire can vulcanized independently `l' ~';'I •'r fastened to the rim at the beaded edges. The See also:Parsons _" non-skid device consists of chains See also:crossing the tire at right angles and fitting loosely over its surface; they are ~1`.• fastened at intervals to two See also:chain rings one on each side of the wheel, and can be easily adapted to any tire. (A.

End of Article: TIRE

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