Favourable Impressions of
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A FAMOUS FOUR -TONNER
Road Test No. 78
4n Example of the Thornycroft DC Type, with Forward Control, Demonstrates its Marked Top-gear Pulling Powers, Lightness of Control ind Moderate Fuel Consumption
FEW manufacturers cater for such a wide range of chassis types as does John I. Thornycroft and Co., Ltd., Thornycroft House, Smith Square, Westminster, London, S.W.1. The range of goodscarrying models includes 19 types, having pay-load capacities from 30 cwt. to 12 tons. One of the most popular is the PC, designed to carry 4 tons. It is made in normalcontrol and forward-control varieties. The concern in question placed at our disposal one of the latter for our usual one-day trial. The actual chassis was one passing through the shops, and had covered only a small mileage in the course of its routine testing.
Weighbridge figures will be found in the accompanying panel; both the bare chassis and the complete vehicle were weighed. With full standard equipment, comprising electric lighting set, electric horn, air filter, speedometer, spare wheel and tyre and the generous tool kit provided, the weight of the chassis —and consequently of the vehicle— would be about 2i cwt. more.
The loading, as the chassis was ballasted for test, worked out at 44 Per cent. front axle and 56 per cent. rear axle. As can be gathered from one of the illustrations, the 16 ft. of available body space was alrno.st wholly occupied by the load boxes. The proportion of the load representing the body (18 cwt.) was the maximum which the maker recommends for this chassis, as was the pay-load.
B28
After checking the weights the vehicle was taken around a 28-mile course in order to test fuel consumption over a route fairly representing average conditions. The route lay through Worting, Deane, Whitchurch, Bullington Cross, Popham Beacon and back ,to the works at Basingstoke.
The normal cruising speed was about 22 m.p.h. and the useful maximum, without adventitious aid, was 30 mph. The latter figure could no doubt be increased with a vehicle well run in. Pulling power on top gear has always been a feature to which the ThornycyV-.:
concern has paid special attention ; in the case of this PC-type chassis it was especially marked. With exception of traffic checks it was necessary to use the indirect gears on only seven occasions in the 28 miles, an unusually low figure for a 4-tonner. Consistent gradients of the order of 1 in 14 demanded the use of third gear, whilst 1 in 10 was comfortably tackled on second. In view of the comparative closeness of the third and second ratios it was desirable to change down before the engine speed fell too low. On first gear really bad hills could be climbed with ample power in hand.
Before setting out on the 28-mile trip the special test tank was charged with three measured gallons of commercial spirit. On the completion of the run the remainder was drained off, measured and poured into the main tank. The quantity actually used gave a consumption rate of 9.49 m.p.g. The average speed maintained was 20.2 m.p.h. This fuel return is about .5 m.p.g, above the average for a vehicle of the 4-ton-pay-load class. During the trip in question the roads were, for a large proportion of the way, wet and in places rather heavy, therefore the rolling resistance was above the normal for the time of year.
The carburetter was dismantled for inspection and the setting was found to be as follows: Main jet, 145; pilot jet, 60; choke, 28; float, 64 gr. This setting, of course, remained untouched throughout the day. During a fine spell the braking abilities were tested. The hand brake, affecting the rear wheels, proved useful when descending long hills and the retardation figures obtained by its use alone are indicative of a good degree of power for a set which is not regarded as the service brake.
The peda 1applied brakes were next tested, and the figures obtained have been used to prepare the appropriate curves in the braking chart. The Westinghouse servo gave a quick response and made the effort required upon the pedal to be of almost negligible proportions. Despite this lightness it was possible to judge by the " feel " of the pedal just how much work was being done by the brakes. Both master and individual adjusters are easily reached and equalization can be effected in a few moments.
Acceleration tests were next completed, but the road surface had become wet ; this condition obtained throughout this section of the trial. Comparing the results of the getaway from rest to 30 m.p.h. with the class curves published in our issue of May 12th, 1931, it is found that the Thornycroft improves on the standard performance for 4-tonners by about 10 per cent.
Throughout the day the normal working temperature of the cooling water was about 160 degrees F. Prolonged hard work had little effect upon the cooling system, which can be regarded as allowing an adequate margin for any reasonable transport work.
During our spell at the wheel we were particularly impressed by the small amount of effort required for any operation connected with the controls. Turning the wheel, either at cruising speeds or while manceuvring, required no more effort than is ordinarily associated with a 30cwt. chassis. The clutch pedal proved to be comparable as regards pressure with that of the average light ear; it could easily ho depressed to the full extent, merely by hand.
As regards the gear change, it may fairly be said that it would be difficult to provide an easier control with the conventional forra of transmission. This applies even with regard to the change from first to second gear ; as the respective ratios are 38.28 to 1 and 18.99 to a rather larger drop than usual —it is a testimony to the design of the gearbox and its selector mechanism.
For checking the vehicle an long descents the . hand ..brake Proved useful, being sweet in
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action, light in application and reasonably powerful. The service brake gave evidence of definite power and was so light in action as to require very little effort on the steepest descent.
A feature of recent introduction consists of the grouping of the ittstrnme.nts in a casing clipped to the. steering column. In this position the various dials are easily seen, and•
the whole unit can be detached quickly if any item requires attention. This system also removes the instruments and their connections from effects due to body motion relative to the chassis.
Under load all four springs were approximately flat, thus causing the smallest amount of movement of the shacklepins in their bushes. Under full load the riding was comfortable, and there was no tendency to pitch, either fore or aft. The strength of the rear springs, coupled with the sweetness of the clutch, prevented any " bucking " when starting from rest or effecting a quick change. Summing up the road performance of the Thornycroft PC Forward chassis, its outstanding characteristic is ease of handling; next is the flexibility of the engine, which is capable of pulling sturdily on top gear or gathering speed rapidly by use of the indirect gears. The fuel consumption, despite the newness of the chassis tested, proved to be better than the average for the class. The hand brake was of practical value for retardation as well as for parking purposes ; the service brake was capable of giving a performance in conformity with modern standards. A survey of the chassis, from the maintenance engineer's viewpoint, is reassuring. All steering components, except the track rod, are ahead of the axle, the box being particularly easy of access. One of the photographs which we reproduce shows the accessibility of the engine details; the sump can be detached without disturbing other chassis parts. The gearbox top plate is of generous proportions and the worm-and-differential unit can readily be lifted out of the axle casing without jacking up the wheels, owing to the use of fully floating shafts.