The N.A.P. " Super-cushion" Tire.
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A Resilient Tread which is Unpuncturable and a.n Effective Non-skid.
What was for long known as the tire problem is not nowadays so intistent as it used to be, that was in the days when solids were with few exceptions unsatisfactory and uncertain as to mileage, and when the cost of pneumatics for anything but the lightest of commercial models was prohibitive. In the early days of bus and lorry operation, tire-mileage costs were nothing less than exorbitant. In a number of bad cases, these amounted to as much as 7d. per mile per vehicle, and even worse records are available. Nowadays wheel treads are nothing like such a source of anxiety to owners. Nevertheless, there is still much room for the inventive faculty, and we are not by any means at the end of the problems which are presented in the search for the most economical and most resilient covering for the rims of road wheels.
The respective proper uses of solid-rubber and of pneumatic tires, so far as the commercial vehicle is concerned, have now been fairly well allocated as the result of experience, and it is generally accepted that the axle weights which are common to vehicles carrying a net load not in excess of 15 cwt. may be satisfactorily run on pneumatics, and that twin tires of that description may yield a load capa-city of perhaps five cwt. more. Over and above such load units, it becomes necessary to use solid tires, bringing with them their limitations in respect of axle and other design. It would seem, therefore, that, while these two broad classes of tire equipment have been developed by the skill of the manufacturer to such a stage that they are thoroughly satisfactory and economical accessories, there is still room for some form of compromise which shall be equally suitable for all vehicles of medium loads, which shall, as a matter of fact, bridge the appreciable interval between pneumatic and solid. There has been in the past a number of attempts to effect this end. Only a few have withstood the ultimate tests of continued and varied employment in other than demonstration service.
A comparatively recent proposal — and, indeed, it is more than a proposal, for it has seen much service
— is the N.A.P. "Pneumatic Tube Tyre." This is a tread which has entirely unconventional characteristics. By means of the special design of the felloe and retaining bands and of the rubber cross section, it has been found possible to produce what we perhaps prefer to
310 call a ' super-cushion " tire, although, of course, its efficiency depends upon the pneumatic action of the air which the rubber construction imprisons. The very peculiar section, which is revealed in one of our illustrations herewith, has been adopted by the inventor as the result of much special experience, and he claims, through the N.A.P. Pneumatic Tube Tyre Syndicate, Ltd., of 4, London Wall Buildings, E.C., that he has secured a number of very definite and practical results. We may mention a few of them as follows : the securing of what is called " high speed of recovery," owing to the special :Section of the tire, which enables it to be run on both driving and steering wheels, at a low instead of a high air pressure; the securing of a high coefficient as between tire and, road surface, no matter in what condition the latter may be, and, therefore, the establishment of great non-skidding properties ; the absence of any canvas, cord or fabric in the construction of the tire ; entire immunity from bursting or puncturmg ; and great facility with regard to mounting and dismounting. The N.A.P. tire is subject to the usual guarantee of 10,000 miles service. We ourselves handled a highspeed, high-powered touring car recently over a very considerable journey during which all classes of road surfaces, in various conditions, were purposely encountered, and we must admit to unqualified surprise at the comfort which was obtainable under all conditions. There was none of the clinging to the road which one would anticipate from a non-pneumatic tire, especially on the steering wheels. Under almost all conditions, with the exception, perhaps, of very badly potted roads with holes at short intervals, it was difficult to distinguish between the comfort of the car as actually fitted and when fitted with ordinary pneumatic tires. Of its non-skidding properties, we can speak in high praise. We found it impossible to skid this particular car, which was a heavy one, on very greasy, badly-cambered roads.
There remains but to say a few words with regard to the mounting and dismounting of this unusual class of tire.
In the first place, it is necessary to have a special type of wheel, with detachable flanges; this wheel is made as a standard by the NAP. Co., and is interchangeable with any wheel, detachable or otherwise, which is on the market today. It is, moreover, ampere tively easy, when making the change, to make the new wheels detachable ; we may also add that the conversion can be made at quite a reasonable charge and with very little loss of time.
The operation of fitting the tire to these wheels is a simple one, and may be best described in conjunction with our illustrations. No. 3 of these shows the process of fitting the contracting band into the tire ; the function of this is to compress the tongues of the tire on to the wheel, thus forming an airtight joint. In the second figure, one flange is being placed in position on the wheel.; the tire is now slipped over the felloe, and pressed on by means of the other flange, assisted by some long bolts; we illustrate this in the fourtl figure. It then only remains to place the 12 bolts in position and the operation is complete. Our fifth illustration shows the N.A.P. tire and wheel complete, adapted to take the place of a Rudge-WEitworth detachable wheel.
The sectional drawings of tires may prove of interest; they illustrate one of its special features, the narrow tread, which is constant under varying loads; the advantage claimed for this is that it enables the tire to cut through mud, and so obtain a better grip on the road surface beneath.