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THE PNEUMATIC TYRE.
How It Has Arrived at Its Present Pitch of Perfection and what are the Causes of the Recent. Rapid Improvement.
THE most outstanding of secent developments in the automobile industry has been in connection with pneumatic tyres. Not only do tyres on touring cars nowadays give two or three times the mileage previously experienced, with much less liability to puncture 'while doing so, but pneumatic tyres can be recommended for much more arduous service than that deemed expedient before the war and withal are giving splendid results in that service. Many of us remember the time when the makers of the pneumatic tyre doubted if it would even stand up to the work demanded from it on .cars. The transmission
of a man's muscular effort from the wheel of a bicycle to the road was then considered to be the limit of capacity of the pneumatic tyre for the transmisson of power.
To-day it is cheerfully recommended for use on lorries of five tons load capacity, vehicles which, when loaded, turn the scale at upwards of 10 tons. It is even being used on steam wagons! '
Not Solely Constructional Improvements.
Whence this improvement? What are the modifications in construction and materials which have made the most recent developments possible —we will not go back to cycling days—and are we approaching finality in this development? An investigation, with .a view to discovering the answers to these questions, revealed at least one fact of which the reader will learn with C28 Surprise and that is that the manufacturers of the tyres themselves only claim a portion of the credit. They say that a good deal of it arises from improved conditions of use and by that they do not, in the main, mean that the better service which pneumatic tyres are giving is chiefly due to the improved conditions of our highways. They actually insist that it is the user himself, by his more reasonable treatment of his tyres and by increased care of them and attention to their working, who is contributing largely to the wonderful results which are now the general experience of motorists as well as commercial motorists. It has been made clear to us, in fact, that in writing an article in which the causes of improved tyre mileage are to be discussed, we must divide our subject into two parts and consider first of all the developments in tyre construction and in the materials used in tyre manufacture which have contributed towards this improve meat, and, secondly, the ways in which users have modified' their attitude towards the tyre to such an extent as to benefit themselves by getting more Julies, many more miles, per pound expended on those tyres.
Pneumatic Tyres to be Encouraged.
We have a twofold reason for dealing with this subject now and in this particular issue of The Commercial Notor. It comes naturally in an " Outlook" number, through which we are looking ahead and trying to envisage impending developments in motor-vehicle design: for we have no doubt that the time is rapidly approaching when a solidtyred petrol-engined commercial vehicle will be as rarely seen on our roads as a steel-tyred steam wagon. Secondly, this issue will be in the hands of our readers when the new scheme of taxation of heavy vehicles comes into force whereby, as regards most heavy vehicles, a rebate of 20 per cent, of the annual licence duty will be made in respect of vehicles which are wholly fitted with pneumatic tyres. We have shown in previous articles how the advantage lies with the pneumatictyred vehicle, even irrespective of this favourable taxation. We are endeavouring now to reassure those who are hesitating on the brink of converting the tyre equipment of their vehicles from solid to pneumatic that they may safely do-so without fear of coming to regret making that important alteration.
Perhaps the best assurance we could give is to point to those , experienced users of big fleets who are making this conversion with all speed. The fact that the London General Omnibus Co., Ltd., after long experiment and trial, is taking that step, should go a long way towards convincing the average owner, and if he insists on an example taken from the ranks of goods-vehicle users we can cite no better name than Pickfords.
Giant pneumatic tyres are not so\ new as many might think. Dunlop was experimenting with them in 1912, but immediate developments had to be postponed on account of an incident which commenced in August, 1914, and kept tyre mannfaeturers, as Well as others, busily engaged in other directions, for a matter of rather more than four years.
In that period, however, developroents had been qu'oceeding in the
United States, and the fact that it was possible to take advantage of the knowledge gained over there contributed largely to the immediate success which followed the introduction of giant pneumatics here and made them a success almost from their inception. Since then improvements have come as the outcome of experience of use..
There have been tremendous developinents in the chemistry of rubber manufacture and this has shown itself in improved blends or mixes of the materials which have contributed towards improved resistance to abrasion, a matter which is obviously of great importance. In addition similar improvement has taken place in the quality of the rubber used between the various plies of the cord which has entirely displaced fabric as a. material for the structure of the Ore itself. The almost universal use of cord instead of fabric is in itself responsible for a good deal of the improved service which we have experienced with pneumatic tyres of all kinds. There is less internal friction, less heat developed,. less disintegration of the material of the tyre because of the absence of excessive heat, and less waste of power in creating that heat.
The Tread of the Tyre.
One outcome of these improvements in materials has been that the tread does not loesen under a reasonable , mileage, given proper conditions of use. This result has also come from improvements in the construction of the tyre with a view to obtaining better adhesion between tread and casing, as well as the use of better materials. As a help towards understanding this, reference should be made to one of our illustrations wherein is shown a cross-section of the tread of a tyre. In that sketch the old type of round tread is shown superimposed upon the modern flat tread. The use of a fiat insteaa of a round tread has contributed largely towards this better adhesion of tread and casing. With a round tread, as will readily be understood, there was more flexion as the tyre came into contact with the road in order to present that proper surface of tyre to support the load. This flexion itself was a primary cause of the tread leaving the easing. In the case of the flat tread the tyre does not need to bend to aeything like the same extent. The area necessary to support the load is almost immediately available and the tendency for the tread to leave the casing is much diminished. Furthermore tile tread is now supported by carrying the material of the tread down on to the walls of the tyre in the form of buttresses. This is shown more clearly in another Illustration of a complete tyre. This buttressing stends to resist the pushbag Of the tread off the case.
'Another advantage of the flatter tread, resulting from the same diminished neeessity to flex, is that less abrasion, less rubbing of the tread upon the road, takes place. Naturally, with a round tread having to flatten itself as the tyre comes into contact with the road and then comes back to the round shape as it leaves, rubbing of portions of the tread upon the road takes place at the beginning and end of that movement. With a flatter tread and less need to flex there is correspondingly less abrasion and, of course, increased life of the tyre.
The design of the moulding on the tread has a great deal more to do with the amount of wear which takes place than many people might imagine. The popular idea is that this moulding is designed with one of two objects in view. It is either devised as a distinctive marking, useful as identifying and therefore advertising the make of tyre, or as a preventive of skidding.
As one example of the ninny factors which increase tyre life, that form of tread which consists of a number of lozenge-shaped projections may be cited. When one of these lozenges make contact with the road as the wheel is revolving, the rubber in it is squeezed forward as illustrated by a sketch, and piles itself up towards the front. The wheel continues to revolve and the lozenge passes rearwards and, as it leaves the ground, shoots back to its original shape, that portion of the rubber which has been piled up at the forward end scraping hard upon the ground as it does so. The consequence, as observant users of pneumatic tyres may have noticed after a time, is that these projections all show signs of wear at the
front end. This "heel-and-toe " wear, as it is called, has been reduced by making use of smaller blocks and staggering them across the tread of the tyre so that their edges overlap circumferentially, or, as in the illustration, by joining some of the blocks up by a thin line of rubber, thus reducing the piling up at the rear edges.
Improvement has also taken place in the arrangement and number of the plies of 'cord fabric of which the tyre is built This is not to say that the strength or efficiency of a tyre is in any way measured by the number of plies, for that is not the case. We mean that the arrangement of these plies has been improved chiefly with the object of providing as much as possible against the risk of what is called a concussion burst. That is a failure of the wall of the tyre brought about as the result of its having at some time come into violent contact with the edge of the kerb or some similar obstruction.
Improved Conditions of Use.
So much for improvements in tyre construction, of which we have only named a few of the outstanding. Much of the increased tyre mileage rEsults from causes outside the control of the tyre makers. First amongst these we must, of course, place iffiproved road surfaces, for there is no doubt that whatever the individual may from time to time have to say about particular stretches of road, the general conditions show a vast improvement upon anything previously experienced.
Then we come to the effect of the better treatment of tyres at the hands of users.• Intensive propaganda on the part of the tyre makers, assisted by the S.M.M. and T., and encouraged by the Press„, has brought users to a tealization of the fact that, comparatively
• minor attentions to the conditions of their tyres and of their vehicle, in so far as its condition affects the running of the tyres, result not only its economy in tyre expenditure itself, but in something more important to the commercial-vehicle user, namely, less tyre trouble upon the road. Space will not permit of more than a brief catalogue of those matters which are germane to this issue.
Foremost comes the necessity of accurate wheel alignment. This is tremendously important and its test and correction are so simple and easy—many tyre service stations will do the work for nothing—. that it is now realized to be folly to overlook it. The question of brake maintenance comes next. Snatchy and irregular use of brakes cause excessive tyre wear, and brakes which overheat as the result of being too closely adjusted cause disintegration of tyres through that heat. Tyres which are underinflated get hot and depreciate rapidly from that cause. Finally, there is that very prevalent tendency to overload commercial vehicles which, if persisted in, has the same effect upon the tyre as regular .under-inflation. All these points, as we have stated, have been brought home to users in one way
or another. It is by attention to them, as Well as by improved tyre construction, that the remarkable mileages now so common with giant pneumatia tyres are achieved..