Types of Rubber Tyres at the Show.
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The weights usually taken by commercial vehicles are generally too large to admit of the employment of pneumatic tyres, so this portion of the subject can be dealt with very briefly. It must, however, be noted that the manufacture of pneumatic tyres is steadily improving, and bringing them within the bounds of possibility for commercial leads. Three makers seem to have experimented in this direction, and their exhibits should be examined by all interested in motor vans. The Palmer Tyre Company is showing a tyre constructed to stand a wheel-load of 25ewt., the Continental Tyre Company one to take a wheelload of one ton, and the Michelin Company a tyre to take a wheel-load of isce-t. In lhis connection the exhibtt of the Stepneywheel in the gallery is interesting : the invention con, sists of a separate rim and tyre complete, the whole being designed for attachment to the existing wheel in a matter of minutes. In the event of puncture, it is unnecessary to stop to effect repairs, as the Stepney wheel can be immediately attached, and the puncture mended at the conclusion of the journey. The owner of every motorcar can appreciate the advantage of this " spare," but with commercial vehicles it is a matter of s. d., as it is no easy matter to remove and replace a tyre cover of the strength and stiffness necessary for use on vans. Every delivery van fitted with pneumatic tyres might advantageously carte a Stepney wheel in some readily accessible positien, i.e., no! under the load. Argyll Motors, Limited, has recently supplied a delivery van on which a Stepney wheat is carried in tile 611b. It is thus stowed above the driver's head.
Looking round the Show to see which of the commercial motors exhibited had pneumatic tyres fitted, the most remarkable are the two vehicles exhibited by the Eastbourne Motor Company. Both of these are fitted with Palmer cord tyres, and in this connection it should be noted that the omnibus, which is a toh.p. eight-seater, has run Owe, . and a half months since it vas supplied to the Chatsworth Hotel Company, at Eastbourne, without puncture or any 'tyre trouble. It is therefore not surprising that the Eastbourne Motor Company feels sufficient confidence in the Palmer tyre to fit it to other vehicles. On the Iris stand (Legros and Knowles) is a laundry van for the White Heather Laundry, of Stonebridge Park, which is fitted with Michelin tyres and Samson non-slipping treads. On the stand of James and Browne, Limited, is an ambufmce van lie, d wirh Michelin tyres, and on the Argyll stand a traveller', van :fitted with Continental pneumatic tyres on the frent wheels. All the other commercial vehicles are fitted with either solid -rubber tyres or steel tyres. Solid rubber tyres have Ill be fitted to a great many commercial vehicles, in preference to iron ivres, so as to obtain the extra speed which is legal under the fIeavy Motorcar Order, when tyres of " a soft or elastic material " are used. Rubber is not the only material that fulfils these conditions, and many other substances have been suggested, but the Olympia Show does not con
thin a single example of such lyres, which is much to be regretted.
The commercial motor user will encounter considerable difficulty, if he hopes to decide on the best tyre to use for his vehicles front the exhibits at Olympia; but a description of the various tyres, from the point of view of their lasting and renewal qualities, is of interest. The quality of the rubber is naturally the most important point, but, as the makers all realise that a high percentage of the gufh is necessary for durability, it may safely be concluded that the exhibitors at Olympia would place nothing on the market unless of the highest attainable excellence. The next question is the ,hapo of the section. Tyres are made in all sorts of
shapes, with fiat treads and with rounded treads, but there is little advantage to the commercial user in a rounded tread unless he is using a comparatively light van or intends to run at high speed. For, naturally, a rounded tread will soon wear flat, and, however nicely the tyre may he rounded when new, it will be flat for the greater part of its life.
Careful measurements of tractive effort have shown that there is a considerable drag with any soft or resilient tyre, and more so in a solid titan in a hard-pumped pneumatic. tyre. This is due to the fact that, as each portion of the tyre mines in contact with the road, it has to be crushed down by the load, whilst it does not spring back again with sufficient rapidity, as the tyre leaves the road, to return any 01 the effort that has been spent in compressing it. There is, therefore, work doneon the Lyre, which means an abseeption nf eng,ine power, even though it may be but a small quantity. As energy can never be destroyed and can only change its form, there is a resultant heating of the tyre. This heating is primarily due to the internal friction of the particles of the rubber as the tyre is compressed and as it regains its shape. It consequently follows that the thicker the tyre the more will be the movement amongst the tyre particles and the greater will be the heat generated. A wide that tyre is, therelore, more economical of engine power than the same weight of rubber in a narrower tyre, and so it is advisable to use as wide anti as flat a tyre as is rommercially practicable. In fact, the designer must put it this way :--If I use too thick a tyre, 1 shah waste engine power, and the tyre will heat; if I use too thin a tyre, I hall not ebsorb the vibration due in roadshocks; if I use too wide a tyre, I shall have to use a heavier wheel; if I use too narrew a tyre it will wear out very quickly : I must, accordingly, strike a happy medium amongst this choice of evils. There is no doubt that, in the past, tyres have been used that were much too narrow, and consequently the wear has been excessive; but few people seem to realise that it is just as great an evil to use too thick a tyre. Much of the difficulty has been obviated by the adoption of twin tyres, but even these are seldom wide enough. The commercial user will do well to select a tyre that presents as wide a surface as possible to the road, and, at the same