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5-TONNER

29th December 1931
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Page 42, 29th December 1931 — 5-TONNER
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OF DISTINCTION pOSSIBLY no maker offers such a comprehensive range of goods models as does John I. Thornycroft and Co., Ltd., Thornycroft House, Smith Square, London, S.W.1. For 1932 the range has been revised, and the KD-type now bears the name "Strenuous." It can be employed as a 5-tonner with a 1-ton body or to carry 41 tons with a tipping body and gear weighing 11tons ; in the latter ease it has a short-wheelbase chassis.

With regard to the test which we carried out the chassis was of the normal-control type, intended for a 5-ton pay-load, and equipped with a platform body and cab. Prior to the test the vehicle had covered some 2,000 miles. In all material respects it was a standard product

Recently introduced details in the specification include the standardi zation of four-wheel brakes operated by Westinghouse servo ; all brakes take effect directly upon the wheels. The springs are now longer than before—the front ones being 4 ft. long and 3 ins, wide, whilst the rear ones are 5 ft. long and 4 ins. wide.

In order to conform with modern ideas of appearance, the radiator is of a new type and the bonnet line has been changed. This does not give an unbalanced appearance, because the wheelbase has been increased and the frame height lowered by 3i. ins. The output of the four-cylindered engine has been increased, and comments upon its performance will be found in a later paragraph.

The Thornycroft Strenuous, as taken over, was equipped with a load of ballast exactly scaling the required 5 tons. The weights were checked on an official weighbridge and the data obtained are embodied in the accompanying panel. The ratio of front-axle to rear-axle weight is approximately 1 to 2.6.

Before specific tests could be attempted it was necessary to get clear of London traffic. This gave ample opportunity for a demonstration of the pulling powers of the 60 b.h.p. engine. On long gradients the actual pace was from 14 m.p.h. to 16 m.p.h. There was no tendency to knock when pulling hard ; the automatic ignition control seemed ideally suited to the performance characteristics of the engine. Except for the test of extremely low top-gear speed, the ignition control was not touched throughout the day.

Other features connected with driving were found to be an exceptionally light clutch and wellgraduated braking control by the pedal which operates the Westinghouse servo. The hand-brake lever being inclined well forward in the " off " position; gives a pull up rather than a pull back, which affords the driver a decidedly better purchase.

As regards gear changing, the setting of the clutch stop was favourable to a fairly slow change, but, of course, this can be altered according to the driver's fancy in order to give a really quick, straight-through change if preferred.

A spring-spoked steering wheel is a refinement which the driver appreciates, and we found that its flexibility in no way impaired manceuvring powers. The ratio of the-steering box is rather high for a 5-tonner, but for main or secondary-road work the standard gear is suitable.

Flexibility on "Top."

A study of the acceleration curves discloses the unusual top-gear pulling powers of the Thornycroft engine. The governed speed on top gear was between 29 m.p.h. and 30 m.p.h. Up to the former figure the governor showed no tendency to interfere and the engine gathered speed smoothly and was completely free from vibration. On the second and third gears the maximum speeds were 9 m.p.h. and 18 m.p.h. respectively, whilst the gear ratios proved to be well suited to the gross weight, particularly if an early change to third speed was made, when it was obvious to the driver that the gradient would require an alteration of ratio. This was not frequently necessary, owing to the aforementioned good pulling powers on "top."

A study of the braking graph shows that the servo-operated fourwheel brakes offer thoroughly satisfactory deceleration. At low speeds the quickestio possible pull-up is afforded by the use of both sets of brakes, as the hand brake counteracts the essential but slight time lag of the servo. At maximum speed, however, the quickest deceleration is obtained solely by use of the foot brake, as the addition of the hand brake merely tends to lock the rear wheels.

Safety in Braking.

For all service braking the fourwheel set, which is pedal-operated, provides all that can be required. When coasting in neutral with the engine stopped and the servo, in consequence, out of action, the retardation powers are good, but, of course, the braking effort on the part of the driver has to be greater. We adopted this plan merely to test the system. Under all conditions braking is effected smoothly ; the holding powers of the hand brake were revealed as thoroughly sound.

When restarting on Cocks Hill, near Elstree (gradient 1 in 6), the first gear of 37.4 to 1 gave a getaway which made one doubt the severity of the gradient, and, at the same time, showed that the name " Strenuous " qualifies rather the type of work for which the vehicle is suited than its impression of performance.

For the fuel-consumption tests :I mixed course was chosen and three measured gallons of fuel were used. The first gallon lasted for 7.7 miles and top gear sufficed throughout, despite hills in the order of 1 in 25. The average speed was 20.1 m.p.h. The next gallon sufficed for 7.4 miles at 17.1 m.p.h. over a hilly route, which included one traffic stop and .3 mile in third gear. Actually, the best result was 7.9 miles on one gallon at 18.7 m.p.h., including .15 mile in third gear and .1 mile in second gear. The radiator was not blanked off for the test and the water temperature, which showed no appreciable rise after the use of the indirect gears, averaged 142 degrees F.

The mean fuel-consumption rate over 23 miles was 7.66 m.p.g., and the average mean speed 18.6 m.p.h., attained at a cruising speed of between 20 m.p.h. and 25 m.p.h., showing that a useful average can be achieved, despite the governor, largely by reason of the marked topgear capacity of the low-compression four-cylindered engine, which is as powerful as it is unobtrusive.

At the completion of the day the carburetter setting was checked and found to be: main jet, 80; compensator, 140; choke, 25. This setting, of course, obtained throughout the day.

Turning circles were measured during the run; it was found that adjustment was required, as the 60-ft. circle, which can be attained, was not feasible at the time owing to the setting of the lock stops.

In conclusion, we summarize our impressions of the Thornycroft Strenuous chassis when carrying its full pay-load of 5 tons.

Three features predominate in that they immediately strike the observer. Hills can be climbed on top gear which call for third gear with most other comparable vehicles. This reduces fatigue on the part of the driver and saves fuel. The latter item is reflected in the fuel consumption return ; economy is the second item. Third, the efficiency of the braking system is an obvious advantage. In every way the chassis is controllable, and the springing deserves favourable comment by reason of its counteracting of violent shocks. A deep pothole produces only a gradual motion of the chassis, so that both load and coachwork are given every advantage.'

In a nutshell, the easy running of the Strenuous chassis completely denies that the adjective in question applies to its own operation or to its driver's task.

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