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NEW TYRES FOR COMMERCIAL VEHICLES.

3rd May 1921, Page 10
3rd May 1921
Page 10
Page 11
Page 10, 3rd May 1921 — NEW TYRES FOR COMMERCIAL VEHICLES.
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Dunlop Developments which Aim at the Improvement of the Solid Tyre. The New "Super Cushion" Solid Tyre and the New Pad Tyre for Agrimotors.

E HAVE lately observed mistaken references to " triple solid tyres and to " cushion " tyres as being products of the Dunlop Rubber Co.'s factories and have accordingly secured permission to deal with the recent developments in tyre design as the outcome of the efforts of the company to improve the solid tyre.

The" twin" solid tyre came into vogue in the early days of the commercial motor vehicle because of the need for spreading the load over a. larger area than was* afforded by any single tyre on the market. The difficulty in the way of making a single tyregreater width than, say, on a. 4 in. base lay in securng satisfactory vulcanization in. the portions of the material farthest from the surface.

But the twin tyre has involved more than one objection. Owing to road camber. and surface inequalities the load is more often than not carried on the one tyre than on both, whilst the space between the tyres is an extraordinarily convenient receptacle for stones and road debris, which become wedged in and cause such damage, that it is safe to say that thetmileage of many a pair of tyres has been cut down by 50 per cent in consequence. Of the tyres e supplied on mileage contracts a substantial proportion is rendered useless by stone damage.

• The Development Department of the Dunlop Rubber Co., Ltd., has studied this question deeply, and, as a result of prolonged trial and experiment, has now placed on the market three new standard sections of grooved tyres of the giant type made from the ordinary or standard Dunlop quality of rubber mixture and three identical sections, made in what is known as the" super-cushion" quality mixture, this being a softer rubber and entailing certain conditions of usage to which we shall refer.

The three diagrams accompanying this description show the sections of the new tyres, from which it will be seen that three sizes now being marketed are the 8 in., which replaces a pair of twin tyres on a base of the same width, the /0 in., and the 12 in.. On the 8 in. section drawing we have superimposed the section of a pair of 120 mm. twin tyres, and it will be seen that by the employment, of a single tyre the

objectionable gap between the twin tyres is filled in and that a greater depth of tyre is acfleided, the outer walls of the) tyro also being faired off. In this way the maximum of load carrying capacity it attained, whilst there is also a maximum of resistance to. abrasive wear.

All the difficulties of vulcanizing to the required depth have been overcome, and the greater depth provided should obviously afford greater longevity to the tyres so that a substantial increase of tyre mileage should be experienced.

Each tyre is moulded with the conventional grooves, in the non-skidding properties of which the average driver of a -commercial motor vehicle has so much confidence. They are of a shape and depth• that will not conduce to the trapping of stones, and the tyres, therefore, will not suffer from stone damage because of the presence of the. grooves. With regard to the "giant" solid tyres made of the "super-cushion" quality of rubber compound, the use of this softer materiel will, of course, give the advantage of smoother running, and the tyres should, therefore, gain great favour with motor coach proprietors, who are not prepared themselves to experiment with large pneumatics, but require something in the way of tyres to live the smooth running that is not afforded by the ordinary solid tyre. Obviously, the Use of a softer rubber compound must entail a sacrifice of some of the load carrying capacity of the tyre, the safe load per unit of area being, perhaps 20 per cent. less. It is, therefore, necessary to Make the area of contact that much greater, so that in place of a pair of twin tyres of 120 mm. section on an 8 in. base, the 10 in. single tyre of " supareushion " quality of rubber should be employed, and as the load would then be spread over the larger area the pressure per unit of area would not be taken beyond the unsafe limit, nor would the abrasive wear be increased.

We look to the new Dunlop solid tyres to replace entirely the twin solid tyres in a very large number of fleets.

Another interesting Dunlop development is the new pad tyre for agrimotors. It will be remembered -that

the Dunlop Co. were assodiated with Mr. Henry Garner in the production of the segmental tyres with Garner's patent method of fixing, adopted for Garner tractprs. The Development Department of the Dunlop (Jo. firmly believe that the future of the farm tractor depends upon the rubber tyre, because fields in this country are -small arid a great deal 01 road travel for all agrimotors is involved, whilst the farmer buying a tractor will always require to 'use it for road haulage as well as for ploughing, cultivating, reaping, and threshing. Thus, the land strake and the road tyre must be readily interchangeable.

Moreover, it is essential that the method of attachment should be simple and absolutely reliable, because any farm implement is apt tobe roughly treated and, between periods of use-, to become neglected.

In the Dunlop Pad tyre, the tyre is made in three segments to fit on the tractor wheel rim, each segment being bolted to the rim by three 2 in. by

standard Whitworth bolts, obtainable at any ironmonger's. The head of each bolt sinks in a square well in the steel band carrying the rubber tyre, so that it cannot turn, a diagonal groove being made across the tyre, at that part.. The head of the bolt at each end of the segments overlaps the endsof the two adjoining segments, so that on a throe-segment tyre nine bolts are all that are required to provide a firm attachment, whilst the job of attaching or detaching is simple in the extreme. The tyre is vulcanised to a steel band aa usual and stands 2fij ins. high from the base. .


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