A NOVEL TYRE
Page 42
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for Negotiating Soft Surfaces
MHE name Roadless Traction, Ltd., is associated in the minds of most People chiefly in connection with the development of vehicles of the endlesstrack type. The company's own conception of its work is, however, that it concerns all means for movement over soft or Tough surfaces, particularly he former, • whether the medium employed he an endless . track or -a wheel, but until some three years ago it was unable to see any real scope in the direction
of employing wheeled vehicles for operating over earth-road surfaces. Such roads, even in their dry condition, will not permanently withstand. a greater pressure than about 15 lb. per square inch.
For many years past, however, the company has recognized that if a tyre could he procluQed which would offer to the ground surface a flat or even slightly concave area of contact at a pressure not exceeding that mentioned, then the scene for the employment of vehicles equipped with such tyres would indeed be great.
Astonishing Results With Soft Tyres.
During 1927 experiments were undertaken in the Sudan by arrangement With the Director of Transport. The experiments proved conclusively that the mere lowering of the air pressure in pneumatic tyres resulted in the most astonishing increase in the efficiency of vehicles operating over soft surfaces. Two similar rigid six-wheelers were chosen, one being provided with tyres pumped to 110 lb. per square inch, and the other with similar tyres, but with the pressure reduced to 20 lb.
On wind-blown sand hills, the vehicle with the high-pressure tyres sank immediately to such a depth as to Make B8 movement impossible, whereas the other vehicle with the same load could travel over the sand hills in second gear.
At Dungeness, over a particularly soft shingle surface it was found that a light vehicle with tyres at a pressure of 5 lb. gave such a large area of ground contact through tyre .deflection that the vehicle could travel over the shingle for any distance. • It became evident that if 'a. tyre could be evolved embodying the characterie
tics outlined and it could permanently be employed at a very low pressure:kit would be possible for a light vehicle to fulfil the essential requirements of earth-road or roadlesi transport. Conventional tyres with merely a reduced pressure cannot be regarded as a satisfactory solution of the problem, as the natural cross-sectional form is approximately circular, whereas the conditions demand that a flat or even slightly concave surface shall be offered to the ground to prevent.flow of the soft surface from beneath the tyre. 'Snow shoes and skis, for instance, are not designed with semi-circular under surfaces which would invite sinkage. There is also the important question cf the vulnerability of the walls when lightly inflated.
With all these factors in mind, Road less Traction Ltd., unnersbu ry
House, Hounslow, Middlesex, has devoted a considerable time to the production of a tyre which will fulfil the conditions. Finality has not yet been reached, and in respect of durability further information is desired, but sufficient progress has been made to indicate that tyres built on these lines are likely to prove a practical proposition.
The new Roadless tyre is known as the " knock-kneed " or K.K. tyre, and reference to our illustrations will show that the name is a most appropriate one.
In the new Roadless tyre the walls are completely protected frOm damage or puncture, the tread iS stiffly reinforced with layers of canvas, and experience tends to show that the puncture trottble istpractically obviated.. It will also be observed that whilst the walls of the conventional tyre do not support the tread, air pressure being entirely relied upon for this purpose, the shape of this Readiest; tyre has the effect of offering considerable support to the tread, apart from any air pressure.
Two of our pictures show the new tyre, one with 20 lb. air pressure and
the other deflated, the difference between the ground contacts being remarkably little, the length of contact with the inflated tyre being 71 ins. and that of thd deflated tyre 1011 ins. It will also be noted that the tyre tread is slightly oeneave, although in the example shown there is a raised pattern slightly convex in form, but for normal earthroad surfaces this pattern could probably be dispensed with. Tests have shown that the Roadlese tyre can run completely deflated with'. out detriment either to the tyre or to the vehicle. Further tests of long duration azt still necessary to ascertain whether the construction and materials: will give long life under these condi, ,tions, but sufficient has already. been done to show that what mo-dificationd may yet be called for are matters more of detail than of principle.
• A Normal Pressure of 10 lb. Quite Practicable. The normal running pressure is
101b. per sq. in. A claim is made that not only will it prevent damage to an earth-road, but that, under all normal conditions, it will have a smoothing and consolidating effect. The form of tread combined with the low pressure increases the overall efficiency when the vehicle is opeeating over soft surfaces, and it would appear feasible tOtrun services under conditions hitherto considered to be impracticable. Experience has already shown that it is possible to retain the tyre against creep, even when deflated.
The form of tyre is open to one ob jection. This is that, owing to the very low pressure offered to the ground, it may not cut its way through a film of greasy clay overlying a com paratively hard ground surface. Ia such cases wheelspin might take place. This cannot be met by increasing the Pressure in the tyre and altering*the form of tread, and, under the conditions described, the remedy is unquestionably the temporary fitting of some anti-skid device in the form of a special tread or chain.
The new Roofless tyre is not at present definitely on the market, but the company will be glad to hear from those who are involved in transport difficulties overseas, where this tyre might alleviate or obviate the trouble.