DEVELOPMENTS IN COACH CHASSIS.
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11\T-spite of the great increase which has occurred in the number of motor coaches operated throughout the country, development in the chassis constructed for motor coach work is not proceeding at the rate of speed which was hoped for by many. At the commencement of the real motor coach movement it was quite understood that the coach chassis could be little other than a very slightly modified. edition of the chassis intended for goodscarrying bodies, and the use of such chassis was enoonaged to a certain extent by the fact that many owners of motor coaches.hoped to be able to employ their vehicles as goods-carrying vehicles when inclement weather rendered the use of the open motor coach practically impossible. Now, however, it is being realized more and more clearly that, generally speaking, the use of goods-carrying bodies on motor coach chassis is not an ideal proposition, whereas in many cases the coach, if fitted with a winter body, can be utilized throughout the year, perhaps not fully during the winter months, but sufficiently. to cover its overhead charges. The goods-carrying vehicle has a somewhat trying time during the winter months, and it usually requires extensive overhaul to render it once more suitable for passengercarrying use.
The adoption of pneumatic tyres • on many coaches has done, and will do, much to cause considerable delriation between the two designs, i.e., goods-carrying chassis and passenger-carrying chassis. T'heehassis advertisfel as being suitable for both purposes is likely to become less and less popular. The coach proprietor wants something:more for his money than a chassis almost exactly the same as that used by the haulier, and he does not see why he should be compelled to run the equivalent of a 4-ton goods-carrying vehicle when the total weight of his passengers is from 30 cwt. to 2 tons.
Pneumatie tyres call for reduced weight, and both combine to raise the speed at which iti is safe for the vehicle to travel. This being the, case, the old gear ratios will have to go by the board, otherwise the engines will soon be knocking themselves to bits. Springing, also, must receive mature consideration. At present far too many of the vehicles are very coarsely sprung, and this is particularly the case where they are designed for dual purposes. With increased speed, more attention must be paid to the question of silence in running, as the low humming given by gears at moderate speed may rigs) to a crescendo at the speeds permitted in the new designs. With increased speed, adequate braking also becomes a vital necessity, and we consider that braking only on the rear wheels will soon prove. quite inadequate. Our views on the subject of the six-wheeled coach have already been expressed in extenso, but we would point out that therein lies a very important development, not only so far as reduction of wear on the roads is concerned, but also as regards the provision of adequate brakes, under which we must not forget to include,sprags. One trouble which has been experienced with many, coach chassis is that the frames are too flerxible, with the result that the body has been relied upon to provide the rigidity required. Now, a coach body is by no means ideal in its capacity for resisting bending stresses, and, if relied upon to do so, straining often ensues and much trouble may be experienced, owing to doors flying open, sagging of the back, due to the weight of the hood, etc. Some designers have attempted to overcome this problem by reducing to thelminimum the number of doors, but this is only a makeshift ; the erux of the problem lies in the chassis, the frame of which should be made strong enough to form a, perfectly rigid support for the body. That this has been realized is shown in one or two of the latest chassis, ;particularly the new Halley, in which the depth of the frame is exceptional for the load-carrying capacity of the vehicle.
Considerable success has attended experiments carried out with super-resilient tyres, which have proved eminently satisfactory, provided that the tyres are of ample width and are not overloaded; if narrow tyres are utilized the rolling action on the tread soon causes the tread and base to separate, but When the correct size of tyre is employed its life is comparable with the ordinary hard solid. For the smaller coaches Macintosh N.A.P, cushion tyres • are often used. Both these and the super-resilient type greatly assist in ileducin,g the vibration and general road shocks on the chassis and thus render possible the redesigning of the latter to meet the new conditions.