GREATER TYRE RESILIENCE.
Page 24
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A Claim to the Production of a Tyre Which is Resilient Under all Circumstances, being Self-accommodating to Load Conditions.
THE ARGUMENT. of a tyre expert, with whom we have recently discussed the question of securing a tyre formation which should give better shock-absorbing qualities than the present solid type is that the solid tyre is incapable of being compressed to a greater extent than one-sixteenth to one-eighth of an inch, and that the circumferential contact of such a tyre is seldom 11W-re than three or four inches and is scarcely increased with any large increase of load.
The conditions under which so many commercial vehicles have to work entail running fully loaded, or quite empty, and with various degrees of loading between the 'maximum and minimum. In addition, there is to be considered the practical equivalent of a sudden. overload, when the edge of a pot-hole is struck.
A solid tyre can only-be, and is; constructed to deal with the maximum overload. If it were made more compressible, by the • use of a softer rubber' compound, there would be a loss of power, because the tyre, at the point of contact with the ground, would spew or spread in advance of the point of contact, tills creating what would virtually be a hill of rubber which the wheel would constantly be compelled to climb. There Would be increased drag from such a tyre and the wear of the tyre would be
excessive. .
When ia lorry is driven with no load, the solid tyre, single or twin, is too hard and, coupled with the fact that the springsare too stiff for the conditions, excessive vibration is transmitted to the chassis.: The speed of recovery of a solid tyre, which is said to be less than 100 to the minute, is then too slow.
• What is really required is that, under a, heavy load, a larger area of tyre tread should be brought into contact with the ground, the tyre to be compressible tit) the extent of an inch or more (which, obviously, would permit the increase of circumferential contact between tread and road surface), whilst, under a light load, the area of contact should be automatically less. Under the impact from the edge of a pothole, the fullest possible area of tyre tread should become instantly available for contact with the ground, thus absorbing the shock. The springing should in fact, be taken as nearly as possible right to the point of ground contiet, so as to reduce the unsprung weight of the chassis. As rubber alone cannot do what is wanted, because it cannot be constraine4 to spew only sidewarda
and rear '
iards a cushion of air offers the way, out, provided the tread can be kept narrow for the greater part of the work, any increase of circumferential contact under increase of load then bringing a greater area of tyre wall into play to carry the/ load, so actually increasing the effective strength of the tyre over the area of contact. The potential increase of tyre width mist, from theaform of the tyre, be held in reserve_, to deal with excessive overloads— road surface, obstructions, etc. At the same time, the important factors of long tyre life and speed of vehicle must., so far from being overlooked, be taken into account with a view to every possible improvement in either or both directions..
. In the United States, attention is being paid to the giant pneumatic tyre, which in its ordinary section partly, if not wholly, meets the requirements. It is due to a Britisher that what he describes as a new principle in tyre construction has been introduced. 31r. E. ,B. Killen haa already played a big part in connection with tyre design. mainly for commercial Vehicle work. Two types of tyres for which he is responsible are already on the market and are rendering good service. But new requirements have led
050 . him further along the path of tyre design and experiment, and certain tests which he permitted the writer to witness recently have created a strong impression that Mr. Killen is on the right road to provide a solid tyre which, having an air space between it and its rim, into which the .tvre can spew, and having a section which is best described as of gable form, to permit much readier sideways spew under excessive overload, shall answer to the requirements to-the apparent greatest possible extent. It can be said, without fear of contradiction, that the demonstration of the capacity of the tyres, made in conformity with Mr. Killen's ideas, to increase their circumferential contact by five tunes and then, under excessive overload, to increase their lateral contact nearly four times, would never have been believed had it not been seen and carefully measured.
The capacity to increase the length of circumferential contact from, say, 3 ins, with no load to 14 ins. or 15 ins, with the fullest load, must give not only greater qualities in shock-absorption but, by bringmg a greater amount of tyre into operation to support the load, give abnormal effective tyre strength. The greater life of the tyre followa, and it does not require argument to show that, with greater resiliency involving no greater drag, an increase of speed must follow. The wide effective tread always instantaneously comes into action when the tyre goes over a pot-hole. Such a tyre then becomes sensitive under a minimum load and acquires increased effective strength with every increase of load. The principle is applicable to pneumatic and solid tyres, and some interesting experiments are now being conducted by important users, because of the value of the principle if it should come up to expectations.
One question arises: Can the new type of tyre be applied to all types of wheels? It is claimed that this problem also has been overcome ba, means of a new type of disc wheel which will facilitate the fitting of the tyres to any type of chassis irrespective of the dimensions of the hub or the type of drive employed.
Fuller details of the invention are promised later, as arrangements for the supply of the tyres are now being ranidly advanced. S. F. L.