HOVERING ON THE 3-TO
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3ORDERIANE
By
P. A. C. Brockington, A.M.I.Mech.E.
What is the Truth of Operators' Criticisms of the Wearing Qualities of Lightweight Vehicles and are Manufacturers to Blame?
FOR the past four months or so I have been trying to test the validity of attacks made by members of the Road Haulage Association, at their 1953 annual conference, on the shortcomings of goods vehicles built to an unladen weight limit of 3 tons. These were in some instances coupled with the criticism that the
vehicles were mass produced. This term no longer carries any stigma and its use is as out of date as the legislation that has established a borderline class of vehicle just light enough to operate legally at 30 m.p.h., irrespective of the load it carries.
As pointed out in "Don't Shoot the Maker " (T he Commercial Motor, October 23, 1953), manufacturers have built the largest possible lightweight vehicles at the lowest possible price. The makers say that the greater the cost saving by advances in mass production, the greater is the allowance that can be made for saving weight by improving the material specifications. Within the scope of existing technical knowledge, wearing properties and other matters normally depend in practice upon the prescribed weight, which is a function of legislation, or the distribution of weight as between one component and another, which is largely determined by the operator's demands.
"Blame the Makers
Few operators would, for example, approve an underpowered vehicle for the sake of a heavier chassis frame. They would prefer to repair a lighter frame at intervals and blame the maker for his failure to provide a vehicle of the same total weight, with a more robust frame, by selective weight saving. This would involve reducing the weight of one or more parts which were not highly stressed under the particular conditions of service, to the detriment of users .who depended upon the adequate properties of such parts to withstand a different set of working conditions. Multiple options could double the cost of a vehicle.
The difficulties with which the manufacture F must 'contend are not disputed by the average operator, but some users suggest that the maker diverts attention from the faults of his pi oducts by overstating his problems. It has been impossible, however, to obtain corroborative evidence in support of these criticisms, which cannot be attributed to weight-restriction problems. The opinion of operators varies with regard to what one maker describes as the "circle of improvement," which must be constantly reviewed if progress is to be maintained.
Great Advances According to Mr. R. W. Amey, of W. C. Amey and Son, Abingdon, Berks, "the advances the manufacturers have achieved in design and development have been very great indeed. The power available from the braking system and the engine, and the capacity of the tyres, can he used to maximum advantage to the extent that
the unladen weight of the vehicle can be reduced." • Although Mr. Amey considers the time has arrived for the regulations to be overhauled and modified, he regards the existing type of lightweight vehicle as one which "gives a very good figure in cost of operation per ton-mile"
A contrasting opinion is held by Mr. J. H. Haynes, managing director of John H. Haynes (Finchley), Ltd., North Finchley, London, N.I2, whose comments in the main relate to tippers. He thinks that operating costs could be much reduced if more substantially built vehicles could be employed. Mr. Haynes states that building down to an unladen weight is the cause of most of the troubles in the operation of his fleet.
After 12 Months
These generally appear after a vehicle has been on the road for 12 months. They take the form of cracked wheels and chassis, excessive wear of brake facings and drums, and broken half-shafts and wheel studs. All these defects, he says, could be avoided if the maker were allowed to build the vehicle "just that little bit heavier and stronger to take care of the stresses and strains."
Light-alloy bodies fitted to some tippers are, in Mr. Haynes' experience, costly in maintenance, because they are not sufficiently robust for the impact of toads dropped from earth-moving machines. Tipping gears are also criticized for their short working life.
The personal opinion of a vehicle designer who has watched and influenced the development of the light motor vehicle from the early days of the industry, emphasizes the importance of cost considerations. "The 5-tonners," states Mr. H. King, superintendent of commercial vehicle design, The Austin Motor Co., Ltd.,
"have been kept, not without a struggle, within the 3-ton unladen class. It is wrong to say that they are not sufficiently robust for their proper use in this country, although vehicles in this class are just a little short of capacity to carry the inevitable overload in some overseas markets, such as Finland, Turkey and East and West Africa.
"A little more weight at critical points could cure this trouble, but who is going to pay? I suspect that critical users will expect a substantially heavier and more robust vehicle at the same price. I don't think they are likely to get it.
With regard to the law, Mr. King has no doubt that the removal of the 3-ton barrier would encourage competition between the makers of medium-weight and. heavy vehicles, to the advantage, ultimately, of everyone.
Commenting on the circle.of improvement necessitated by an increase in the output of a power unit, Mr. E. B. Stead, technical director, Albion Motors, Ltd., observes that this is likely to be detrimental to the weaker parts. He also points out that the inter-relation of auxiliary components is such that, when a rigorous weight limit is imposed, any improvement in one detail may adversely affect some other items in the chassis assembly.
That the faults mentioned by Mr. Haynes all developed at about the same time, was described by the distributor of a long-established make of light vehicle as a compliment to the manufacturer. "It is never economic for one part to be built stronger than the others," he said. "A life of 12 months between overhauls may be considered satisfactory under the conditions in which some tippers operate."
Of all the components mentioned at the R.H.A. conference and discussed at informal talks between hauliers, the wheels and brakes fitted to lightweight vehicles have been subjected to the most severe criticism.
Two-piece Wheels
Referring to the strictures of two-piece wheels. Mr. R. C. Reeve. of Joseph Sankey and Sons, Ltd., says that there is ample evidence to show that they are fully satisfactory in service when used in conjunction with the correct tyre equipment for carrying rated loads under conditions for which they were designed. This statement is qualified by the observation that discussions regarding two-piece wheels in the past have been mainly concerned with the near-obsolescent flat-base type, which is often used for higher operating loads than are recommended by the makers. Many hauliers have failed to appreciate the value of recent developments, says Mr. Reeve, the most important of which, he claims, is the introduction of the wide-base wheel of both two-piece and three-piece types. In the Sankey range a flange-and-lock-ring combination can be interchanged with the spring flange for the conversion of a two-piece to a three-piece wheel. The increase in weight varies between 4 lb. and 41 lb. per wheel.
According to Mr. Reeve, there have been no complaints of any kind regarding the wide-base wheel, which, vehicle manufacturers say, provides an increase in mileage life of 10-30 per cent. The average difference in weight between a two-piece wheel of the type fitted to a standard 5-tonner in the 30 m.p.h. category and a three-piece wheel fitted to a normal 7-8-tonner is about 8 lb. to 8f lb. A well-known tyre manufacturer gives the difference in weight of the two tyre sets at 20 lb. to 40 lb., depending on the equipment used.
The fault of the law in permitting operators of fourwheeled vehicles of under 3 tons unladen weight to carry a 9-ton payload, whereas more substantially built vehicles are not allowed to carry more than 7-8 tons, is mentioned by Mr. G. Baird, technical director, Girling Ltd., as a weakness in legislation. In his opinion, operators must be held responsible for restricting the payload to that recommended by the vehicle manufacturers.
Brake Weights
Mr. Baird states that the weight of a set of brakes for a vehicle of 3-ton unladen weight is about 160 lb., whereas a brake set for a vehicle with a gross weight of 12 tons is 210 lb.
Mr. King gives a figure of 2 cwt. for the additional total weight of the heavier frame, springs and brakes which would satisfy the operator who wants a more robust vehicle; an oil engine in place of a petrol unit would increase the weight by a further 2 cwt. and the weight might be raised by a similar amount by fitting a two-speed axle.
A comprehensive list of weight-saving measures is given by Mr. A. J. Smith, chief engineer, Commer Cars, Ltd. These include the use of wide-base wheels, groovedsection spring leaves, high-grade steels and light alloys; the development of plastics is a long-term possibility which is being watched. Knowledge of the precise function of various components, and of the stresses that each member takes, has, Mr. Smith states. fostered weight reduction and economy in production.
The wide-base wheel provides greater rim strength, an improved " ride " and a better tyre life with little or no increase in weight, and represents an important advance over the old flat-base type. The three-piece wheel is offered to operators by the Commer concern
for particularly arduous conditions. The groovedsection spring enables about 1 cwt. to be saved on a typical 5-ton truck.
Incentive to Makers Removal of legal restrictions would not, in Mr. Smith's view, necessarily eliminate the operator's troubles. It would allow weight to be added where necessary, and this would be an important consideration in designing lightweight chassis which were in competition with American vehicles. The incentive remains, however, for the engineer to keep vehicle weight as low as possible. The operator is in business to make money and his revenue is determined by the payload he can carry, his running costs and the speed at which the load is delivered.
" Overloaded, underbraked, undertyred, overbodied and overpowered," is the description used by a tyre distributor of some of the sandand coal-carrying vehicles seen on the roads. "The operators of such vehicles," he states, "are unscrupulous in evading the law by temporary measures designed to reduce the unladen weight of a vehicle when it is checked by the authorities. In these circumstances, I think, it is useless to give advice based on technical or legal recommendations.
"Loading and speed laws should be more rigidly enforced in the interests of the vehicle maker and the operator himself, not to mention other road users, whose lives are endangered. Heavy loads must be carried by heavy vehicles."
Overloading is, in the view of Mr. N. Tattersall, chief engineer, Leyland Motors, Ltd., a condition which must be accepted by the vehicle designer. Additional weight is, he says, necessitated by this condition if the vehicle
is to give satisfactory service. With regard to cost saving, Mr. Tattersall cites the policy of his concern of building the vehicle for the home market dimensionally the same as the overseas model; in this way it is possible to increase the quantity in production. The smallest Leyland vehicle has an unladen weight in excess 01 3 tons.
lightweights for Youngsters Reverting to the opinions ot operators, Mr. Amey indicates an important factor in the reputation of a vehicle in the comment that concerns tend to employ their most experienced drivers on the heavier class of vehicle, whereas, a fair proportion of lightweight vehicles is driven by youngsters with less experience in roadcraft. He also observes that " get-rich-quick " businessmen invariably choose the light vehicle for transport.
After describing the lightweight vehicle as a boon to operators, Mr. L. W. Ballard, of Shipman's Garages, Ltd., St. Margaret's, Twickenham, criticizes the frequents, practice of bodybuilders of "exceeding reasonable limits." This results in top-heavy loads, which make steering difficult and cause accidents, as well as creating excessive stress concentrations.
A well-known bodybuilder in the Midlands agrees that the weight restriction encourages the construction of uneconomic and unsafe bodies, but hotly denies that members of the bodybuilding industry can be held responsible for design or constructional faults. "We are the people," he says, "upon whom, in many cases, rests the last hope of keeping the vehicle weight within the 3-ton limit. Light-alloy construction often helps, but, of course, we cannot always build the bodies as we think they should be built.
30 m.p.h. Up to 4 Ions
" The stage has been reached when the enforced policy of makeshift is detrimental to everyone, but removing the 20 m.p.h. limit altogether is obviously not desirable. We have benefited from compromise in the past—the present lightweight vehicle is a first-class machine—so let there be an up-to-date compromise. The solution of the present troubles is to raise the speed limit to 30 m.p.h. for all vehicles of under 4 tons unladen weight."
It is, perhaps, appropriate that this bodybuilder should have the last word. He is a specialist who tries to satisfy dindividual requirements by giving mass-produced vehicles a hand-made finish. He suggests that "pride in what you buy makes the vehicle last longer and cuts costs."