The Need for Improved Vehicle Suspension.
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DRACTICALLY every commercial motor vehicle on the road to-day is equipped with springs between its chassis and wheels which, in their essential features, are almost identical with those employed for hundreds of years on horsed carts and even on hand barrows. Are we consequently, to believe that what was ordinary practice so long ago is indeed the best to meet modern-day conditions of service?
It is interesting to study some of the reasons for the survival of the leaf spring which has, so far, proved the fittest type. Originally adopted for the motor vehicle, together with many other points in horsed-carriage design, its comparative simplicity and its inherent quality of self-damping, through the friction which occurs between the leaves immediately the springs begin to flex, have given it a decided advantage over other forms of suspension. . .
It is always difficult to displace anything which is old-established. Possession is nine points of the Jaw, and the laminated form of spring has had possession for so long that it is apt to be looked upon as something which cannot be displaced. It may be that a better means of vehicle suspension will never be found, hut if this be the case it is essential that the laminated spring should receive more attention both in its construction and its method of application, for there are extraordinary differences between the degrees of comfort and easy riding afforded not only by vehicles of different makes, but by individual products from the same factory.
The problem of providing really satisfactory springing for a commercial vehicle is considerably more difficult than in the case of the suspension for a private car, as the ratio of pay load to unladen weight varies to a much greater, degree. A fairly heavy commercial vehicle will carry a load approximately equal to its tare weight, whereas a private car practically never carries more than half its unladen weight, and more frequently somewhere about one third. This brings into prominence the necessity for providing a form of springing which shall be adjustable to load, this, preferably, being carried out automatically and so rendered Independent of the factor of human error.
It may be thought by some that a little extra vibration in the case of a commercial vehicle may not be of extreme importance, but we must remember that the commercial chassis is not only employed for carrying goods ; it is now used to a huge extent for the conveyance of passengers, and those al7 who, ride in busel, and particularly in coaches, expect practicaly the same degree of comfort as is afforded by the modern private car. Vehicle speeds have, been increased all round during the past few years, and here, again, is a factor which calls for more resilient suspension.
Bound up intimately with the question of springing is that of damage to road foundations and wear on the road snrfacings. The better condition of our roads in general should not be treated as an excuse for paying less attention to the problem of springing, for the impact of heavily laden wheels which bounce instead of following slight road inequalities may reach a very high figure and result in rapid road destruction, quite apart from the surface abrasion which is undoubtedly caused by arresting wheel spin.
The main factors which have to be considered In designing any form of vehicle suspension are safety, comfort and easy. maintenance. Pitching, bouncing and side-rolling must be reduced to the lowest extent. The spring periodicities must be so judged and arranged that oscillations of increasing magnitude are not set tip and, in general, the suspension of a vehicle must not be an afterthought, but must be treated as an essential part of the whole design. The disposition of the load, the type of body fitted and the nature of the tyres employed all exercise their individual effects for Which allowances must be made.
We are convinced that vehicle suspension has 'not progressed to anything like the same degree as have other details of the chassis, and we would advise designers and all others concerned in the production and use of commercial vehicles to turn their attention to this most important subject. We shall be pleased to ventilate views on this matter from our readers and will, from time to time, deal with the problem from its various aspects.
Bus and Coach Speed Limits in the Projected Motor Bill.
WHEN the long-promised and much-delayed Road Vehicles Bill engages the attention of Parliament, the first section to be dealt with will, in all probability, be the part dealing with publicservice vehicles, largely because the amendments to the present law concerning them will be less controversial than those which will concern the private car and private motorist, whilst it has to be admitted that the need has been disclosed for regulations that will afford greater security for the passengers who use public-service vehicles. Such, however, is the reasonableness of the leading caterers, and so receptive are the manufacturers of vehicles of ideas and suggestions which are the outcome of experience, that all the projected regulations stand a good chance of being anticipated. That, however, is by the way.
Qne of the subjects to be dealt with in the Bill will probably be that of the speed of motorbuses and coaches, now, of course, limited to 12 miles :per hour. It is an obvious fact that the motor coach, since it emerged from its chrysalis stage, has been the most unblushing of all breakers of speed regulations. it has asked and been accorded (by the absence of repressive police action) the right to travel as fast as the private car, and one might say, almost without question, that no motor coach Is ever restrained in its speed to the legal limit. The daily Press has lately been anticipating the terms of the new Bill, and suggesting that an increase in the legal limit for buses and coaches would raise it from 12 m.p.h. to 15 m.p.h., the consideration for this " concession " being an obligation that the law would be strictly observed and enforced.
A speed limit of 15 m.p.h. for buses (or, better still, 16 m.p.h.) would be reasonable and practieB18 ally in accordance with present-day practice. Such an average speed in urban traffic conditions would not be exceeded, and the gain to the travelling public would be the removal of the need for the buses to crawl over the last mile or two of each journey when traffic was light, as in the evenings. This crawling, particularly when a railway station is on, or at the terminal of a bus route, is excessively annoying, involving the loss of train connections to an extent greater than is realized.
A 15 m.p.h. limit for motor coaches, however, would be absurd, and would inevitably fall into disrepute and be disregarded. It is a mistake to place on the Statute Book .enactments which are behind the times, and which do not accord with general habits, methods and customs, because they do no good, and merely bring the law into contempt. If the speed limit is not left as at present, with custom decreeing it as dead and no longer operative (this course finding advocates among those who prefer the ills they know to others they wot not of !), it should be set at such a level as would accord with custom, and it would then court compliance, with public opinion supporting it. A speed of 25 m.p.h. would not be an unreasonable limit, but to set 15 m.p.h. as the maximum would be futile and foolish.
Licence Duties on Six-wheeled Vehicles.
MHE coming of the six-wheeler, both of the rigid-1frame type and of the articulated type, disclosed the fact that the licensing categories were not capable of embracing it, and the licensing authorities had to seek the assistance of the Ministry of Transport In the interpretation of the regulations. For some time the articulated, or " Scammell," type of vehicle has been licensed on the basis of a vehicle drawing a trailer, and this, in the absence of a separate category, may be taken as the most reasonable allocation to a class under the Finance Act of 1920. We have already stated that it has been decided that, under the scale of taxation which comes into force on January 1st next, the articulated six-wheeler shall be taxed at £54 per annum provided the tractor portion, unladen, does not exceed 4 tons in weight. The tax on a vehicle of less than 4 tons unladen weight will be £48; with £6 additional duty for drawing a-trailer, the sum of £54 is reached as the total yearly duty." As the tractor portion of an articulated six-wheeler carries a portion of the load, it is justifiable to term it a " vehicle " and not a "tractor."
What is now required is the official adoption of an attitude towards the rigid-framed six-wheeler which shall encourage its development. We hold that the carrying of a given load upon three axles is better for the roads than carrying it upon two axles. The road surface suffers to a materially lessened degree from the fact that, with four coupled wheels, wheel slip, to all intents and purposes, is impossible, whilst the use of two axles at the rear of the vehicle by spreading the load must conserve the foundations, and, as there is no demand amongst road engineers for lower axle weights, the natural corollary would be the granting of the right for each of the two coupled rear axles to carry the present maximum axle load, which would suggest 12 tons as the maximum useful load for a three-axle vehicle.
There is every reason why the six-wheeled vehicle should be encouraged. Considerable economy in transport charges is attained by the use of one vehicle (with six wheels) in place of two vehicles (each with four wheels, or eight wheels In all), the labour bill, garage charges and many overheads being the same if 12 tons be carried as if 6 tons constituted the load, whilst the cost for consumables—petrol, oil and tyres—would be but slightly more.