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YOU NEED TO KNOW ABOUT

9th February 1973
Page 46
Page 47
Page 46, 9th February 1973 — YOU NEED TO KNOW ABOUT
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SELECTING THE RIGHT VEHICLE FOR THE JOB

THE ART of choosing the right vehicle for the job — vehicle selection — is continually becoming harder and yet at the same time more important to get right. Many commercial vehicle salesmen these days are trained to give a consultancy service, but ultimately it is the operator's money and he must make the final choice of vehicle.

In the lightand medium-van range choice is limited between car-derived vans up to about lOcwt payload and larger vans with up to about 35cwt payload. The choice between the two should be easy to make but at the heavier end of the range the choice between a petrol and a diesel engine may not be so easy.

Price is not really a deciding factor as diesels are not all that much more expensive; a diesel Transit for example is only about £200 dearer than the petrol equivalent and in the slightly heavier Mercedes Benz Transporter range the difference is in the region of £100.

Fuel consumption is a factor but only if big annual mileages are envisaged. On a CM comparative test of petrol and diesel Mercedes vans the difference in average fuel consumption was only 3.1 mpg (17.6 mpg diesel, 14.5 mpg petrol). Assuming a 20,000 annual mileage the difference in the fuel bill would be only £80. However, at 50,000 miles a year the saving would be £200, and at the higher mileage the more robust diesel engine which needs less attention and maintenance, begins to score over the petrol engine.

First cost = minor factor This example begins to point to a truism that few hauliers seem able to accept, particularly with the heavier vehicle, that the first cost of the vehicle is a relatively minor factor in the overall costs. Far too many operators argue about £20 here and £50 there when they buy the vehicle and fail to realize that the price of the vehicle and more goes out in wages, fuel and maintenance to keep that vehicle on the road in the years to follow. For this reason the vehicle specification should not be skimped; it is better to over-specify than to under-specify the vehicle.

Own-account operators are fortunate inasmuch as the load is probably regular and the operation well known, but this is not the case with hauliers and it is important before specifying a chassis to decide what the most useful vehicle will be. Light goods could use a maximum volume body and heavy goods might be able to make use of the shorter wheelbases introduced in last year's revised Construction and Use Regulations.

In the 32-ton-gcw top weight class, good use can be made of the drawbar combination which offers 48ft of deck length against the maximum semi-trailer length of 40ft. If the load is not limited by weight the drawbar offers 20 per cent more volume with very few disadvantages. The drawbar outfit is more stable and comfortable to drive than an artic, and can offer a dual role.

Rear overhang In specifying any bodywork it is important to keep the rear overhang as short as is consistent with a reasonable manoeuvrability because the front axle(s) runs the risk of being overloaded with the vehicle in the part-load condition.

It is not only an offence to exceed the plated gvw of the vehicle, it is also an offence to exceed the plated weights of the individual axles, and this type of offence occurs most commonly on four-wheeled vehicles with so-called "dead-split" axles.

Dead-split axles have plated weights which add up to the plated gvw of the vehicle, and a typical example of this is a 16-ton-gvw vehicle which has a 6-ton front axle and a 10-ton rear axle. In practice it is almost impossible to load a dead-split axle vehicle to its maximum gvw without overloading one or other of the axles. Even if the vehicle is properly loaded when full, usually the removal of only part of the load from the back of the vehicle is sufficient to overload the front axle.

The only way around this problem is to ensure at the time of specifying the vehicle that the axles give a reasonable margin. In the case of a 6-ton payload (9.5 tons gvw) vehicle the minimum — dead-split — weight would be 3 tons front and 6.5 tons rear, but it would be much better to specify axles with a half-ton tolerance, ie a 3.5-ton front and 7.0-ton rear.

Bodywork, again, must be suited to the particular operation in mind, but the type of construction can vary. A strong body will reduce payload and vice versa, and similarly aluminium will give an increased payload as compared to steel, but almost certainly at greater cost. The final choice will be a compromise between payload capacity and durability.

Flooring Flooring must be strong enough to stand any point loads likely to be imposed; these may be the edge of a full 50gal drum of paint or the total weight of a loaded fork-lift truck. Headboards, too, need to be strong enough to prevent the load from shifting under heavy braking. The new DoE Code of Practice: Safety of Loads on Vehicles (HMSO, 30p) is a useful book to study when specifying vehicles and equipment.

The mounting of the body on to the chassis is important, as all chassis are designed to flex under heavy loads. If a rigid structure such as a tank or box body is rigidly mounted to the chassis an area of high stress will be induced just behind the cab, which could cause cracking of the frame.

Having decided on the general payload and therefore weight of the vehicle, it is worth spending a little time to consider performance. Basically this problem points to one of horsepower — how much do I need to give me the performance I want, and what will be the effect on fuel consumption? Drivers like plenty of horsepower because it makes the vehicle easier to drive, and many operators do not like horsepowet because they believe it leads to fasi vehicles which deteriorate rapidly anc use more fuel than need be. In fact the horsepower requirement will be resolvec

to a large extent once the operation is known. Operators who work in North Wales or Scotland will automatically go for more horsepower than those who work in East Anglia.

Under current legislation, new diesel-engined vehicles must have a minimum of 6 bhp per ton and in fact most vehicles up to 16 tons gvw have considerably more than this figure — the Ford D1010 10-ton-gvw-rigid has 10 bhp /ton, for example. It is in the top end of the vehicle range at 28, 30 and 32 tons where horsepower is on the limit. Generally speaking, bigger engines are• available but operators do not specify them.

Fuel consumption

Looking through CM road tests of heavy vehicles, it appears that the fuel consumption of, say, a 260 bhp 32-tonner is not significantly higher than one at 200 bhp, but journey time for the bigger engined vehicle is considerably better. Fuel consumptions may vary up to 10 per cent, but with fuel costs only representing 30 per cent of the total, this represents just 3 per cent of the total running costs and should not be significant.

Many operators feel that torque is a more relevant measure of engine power than horsepower, but the two are linked in an equation by a constant and thus the two are commutable. Horsepower is the rate of producing torque and, for example, an engine producing 200 lb ft of torque at 1000 rpm gives the same horsepower as an engine producing 400 lb ft of torque at 500 rpm.

For this reason a high-revving V8 engine producing high horsepower and

low torque can produce the same performance as an in-line six-cylinder engine producing a lower horsepower and a higher torque. The proviso is that the gearbox and rear axle ratios are properly chosen to suit the individual engines. Generally speaking, the six-cylinder engine would use a six-speed gearbox with a high rear axle ratio whereas the Vee engine would use a 10-speed gearbox and a lower rear axle ratio.

Rear axle Generally, any vehicle can be geared to run at 60 mph if the correct rear axle is specified, because in most cases sufficient horsepower is available, but hill climbing performance is always limited by the horsepower available. If a wide performance range is required, ie 60 mph top speed on the one hand and a 1 in 6 climbing ability on the other, the necessary gearbox spread will increase as vehicle gvw increases and decrease as engine horsepower increases.

Ford runs a very comprehensive training scheme for its commercial vehicle salesmen at a training centre in Essex, where they are taught how to apply such calculations to everyday situations.

Generally speaking, the in-line engine has a better life than its V8 counterpart because it operates at lower speeds, but the Vee engine has the advantage of being lighter for a given horsepower and needing in turn a lighter transmission and axle.

Having considered the chassis, the body and the payload, let me finish by considering the driver. Without doubt the best way to keep a vehicle in good

condition is to keep the driver happy and in the context of new vehicles that can best be done by providing a good standard of driver comfort.

Driver's seat The all-important area is the driver's seat and its relation to the steering-wheel, pedals and instruments together with visibility. The seat is particularly important as the driver spends so much time in it and can dramatically affect his performance. A good seat is fully adjustable for height and reach and would have an adjustable back rest. Ideally also, it would be covered in a breathing fabric material for comfort.

Pedal .pressures and steering efforts should be low; particularly if the vehicle is to be used mainly in traffic, automatic transmission should be seriously considered for light delivery vehicles. All vehicles should have good fresh-air heaters and trunking vehicles should also have good ventilation for use in hot weather.

A small point, but none-the-less important, is that all vehicles, particularly the heavies, should have good windscreen wipers and washers preferably on a combination switch for easy operation.

Tilt cabs have the advantage of one-piece floors which exclude the noise and smell of the engine and also, of course, provide much better access to the engine for servicing.


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