W HILST one would not choose a dreary wet day in
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November to carry out a road test of a commercial vehicle, driving under such conditions brings out more in a machine than a similar test in favourable weather. On our recent visit to Wolverhampton, to take over a Guy Vixen 4-tonner, it rained incessantly the whole day, but what the weather lacked in brilliance was compensated for by the fine performance of the vehicle.
Before dealing with the road test, it would be as well briefly to go over the specification of the Vixen chassis, of which there are three types of essentially the same design, but having different lengths of wheelbase. The one we handled has a wheelbase of 13 ft. if ins., and is built to a gross laden weight limit of 6 tons 15 cwt.
It is powered by a four-cylindered petrol engine developing 60 b.h.p. at 2,400 r.p.m., and giving a maximum torque of 165 ft.-lb. at 1,400 r.p.m. The drive is taken through a single-plate dry clutch to a four. speed gearbox having constant-mesh wheels for third speed, and thence by a two-piece propeller shaft to a spiral-bevel-driven rear axle. Layrub universal joints are used, and the centre bearing is mounted in a resilient self-aligning housing.
Brake Frictional Area 252.8 sq. ins.
The brake pedal operates shoes in all four drums, the system being of the Lockheed hydraulic type. As is general, the hand brake takes effect on only the rear wheels. Drum diameters are, front, 14 ins, and, rear, 16 ins., the total frictional area being 252.8 sq. ins. The front semi-elliptic springs are anchored at the rear and shackled at the front, whilst those at the rear, which are underslung, are anchored at the front ends and shackled at the rear. Cam and roller-type steering gear, 32-in. by 6-in, high-pressure tyres, and 12-volt electrical equipment form other main features of the Vixen chassis.
The chassis weight of the model under test is given as 1 ton 17i cwt., and the total weight as tested was 6 tons 17 cwt. 3 qrs.-2 tons 5 cwt. 2 qrs. on the front axle and 4 tons 12 cwt. 1 qr. on the rear axle. The stretch chosen for the brake tests is some distance from the works on the Cannock Road, and this preliminary run served to show that the cab is extremely comfortable, the engine particularly lively, and that, although a full forward-control machine, conversation could be
carried on almost normally, and there was no suggestion of fumes or undue heat getting into the compartment.
A wet concrete surface is far from ideal for testing braking, but the Vixen produced some excellent figures. The first runs were at 20 m.p.h., from which speed the machine was brought to a standstill in 23 ft. in one direction and 21 ft. 6 ins, in the other, the respective efficiencies being 58 per cent. and 62 per cent. The wheels picked up, as was only to be expected, and the rear of the vehicle slid slightly towards the gutter.
The first figure obtained, from 30 m.p.h., was 44 ft., but two further runs produced stops in 33 ft. and 32 ft., the mean efficiency figure being nearly 84 per cent. —an exceptionally good performance. On all occasions the wheels picked up, but this was unavoidable on such a surface.
A Responsive Power Unit Some idea of the liveliness of the engine may be gathered from the acceleration figures which were obtained from 0 to 30 m.p.h., through the gears, and using double-declutching methods on the first run, slightly uphill, we obtained a figure of 41 secs., which, on a second run in the same direction, was reduced to 33 secs. In the opposite direction 30 m.p.h. was reached in 29 secs. From a rolling start at 20 m.p.h. the Vixen reached 30 m.p.h. in 11 secs. in one direction, and 20 secs. in the other, the difference being caused, of course, by the gradient.
From the Cannock Road we drove out towards, Bridgnorth, our objective being a hill known . as the Hermitage. It is about three-quarters of a mile long, has two easy bends, and finishes with a gradient of about 1 in 8. From a standing start, the Vixen made an excellent climb in second gear, the speedometer showing a minimum of 9 m.p.h. The elapsed time, from start to finish, was 2 mins. 55 secs., showing an average speed of about 15.42 m.p.h.
Atmospheric temperature was 56 degrees F., and the cooling water registered 166 degrees F. at the finish of the climb.
The ability of the hand brake to pull up the vehicle when rolling backwards down the 1-in-8 portion was convincingly proved, as was the extent of the reserve power of the engine in getting away from rest on the same gradient.
A 1-in-3i gradient, with full load, is claimed as being negotiable with this vehicle, and we have no reason to doubt that the Vixen could substantiate this, for at no time during the whole of our run did the engine show any sign that it was not complete master of the job in hand.
A claim is also made for its flexibility, so we kept the speed down to 12 m.p.h. on top, from which speed it would pick up just as readily as it would carry on pulling without signs of distriss.
On the run out to the hill, the Guy test driver repeatedly sent the speedometer over the 50 m.p.h. mark, the springs flattening out the bumps and gullies, to give a smooth, vibrationless ride. General stability is excellent, too, for, despite the many occasions on which the machine could not have been blamed had it behaved in an ungentlemanly"manner, we can pass out its road-holding and general handling qualities as being all one would expect from a good machine.
A run back to the works completed the morning session, leaving the petrol-consumption test to be undertaken in the afternoon. For this purpose a "bottle," to hold one gallon of fuel, was coupled up after disconnecting the lead from the Autovac. The route chosen was comparatively level, and only one change of. gear was necessary, and this at a " Halt " sign. On the outward run, which was covered at an average speed of 27.16 m.p.h., the Vixen covered 13.75 miles, and on the homeward run, at an average speed of 30.09 m.p.h., the gallon of fuel ran out after we had
covered 13.25 miles—a mean average of 13.5 m.p.g. The total mileage covered during the test was 78 miles, the speedometer reading of 117 miles representing the total mileage, covered by the machine.
The exigencies of the moment do not permit a vehicle maker to run prolonged road tests of his own before handing a machine over, and hence it may be taken that any figures which we obtain can be equalled or improved upon after a useful mileage has been covered.
Braking, for instance, should be far more efficient when all the high spots have been worn off the facings, and fuel consumption should show a slightimprovement when the chassis frees up.
If we have seemed eulogistic regarding the performance of the Guy Vixen, it is because we were impressed by its capabilities. It is a particularly easy vehicle to handle, both seats can be reached without performing acrobatics, and the general comfort for both driver and mate could scarcely be improved upon.