Mastiff on the Motorway
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Running at 20 Tons Gross Weight, Thornycroft Mastiff 6 > 2 Achieves Average of 37.4 m.p.h.
Over 107 Miles
By John F. Moon,
A
AN average speed of 37.4 m.p.h. maintained between Birmingham and London is good going for the average private car, and most light and medium commercial vehicles would be hard pressed to approach such a figure. That such a speed was maintained over a distance of 107 miles by a Thornycroft Mastiff 20-ton-gross six-wheeler shows that this vehicle must rank as the fastest British heavy-goods design in current production.
Equally remarkable, however, is that this average speed was accompanied by an overall fuel-consumption rate of 9.7 m.p.g. This gives a time-load-mileage factor of 7,319, an exceptionally high figure for trunk operation in this country, with a payload of 14 tons.
A run of this nature was made possible, of course, only by using Ml, and further emphasized the advantage of such a road with respect to increasing traffic speeds between Birmingham and London. The vehicle used was a standard model as tested by The . Commercial Motor (November 6, 1959). The only difference was that instead of the 6.14-to-1 rear axle fitted to the vehicle as originally tested, a final-drive ratio of 5.375 to 1, available as an option, was employed.
Over 60 m.p.h.
This high-ratio axle yields a maximum speed of 615 m.p.h. when the overdrive gearbox is fitted, and increases the directdrive speed from 40 m.p.h. to 50.5 m.p.h. Tractability and gradient performance do not appear to suffer unduly from the use of the higher ratio, and the Thornycroft was found to be docile in heavy town traffic.
The performance suggests that the 5.375-to-1 axle could well be adopted as standard for most normal haulage conditions, and that the 6.14-to-1 axle is necessary only when prolonged hilly working is expected.
It had been intended that speed and fuel-consumption figures be taken between London and Birmingham as well El 2 as over the return journey, but unfortunately the fuel-test tank had a defective tap which caused an air leak to develop while running northwards on MI.
Therefore it was impossible to make a non-stop northbound journey, although figures were taken for the fuel-consump tion rate between central London and the start of Mb, with a further figure between M10 and the fuel station at Watford Gap.
These showed that the Thornycroft covered the 20.35 miles between the Temple Press car park in Clerkenwell and the Park Street access to Mb O at an average speed of 19.9 m.p.h. and a consumption rate of 7.2 m.p.g. The figures are even more praiseworthy in view of the fact that Central London was left at 8.30 a.m., when traffic was at its heaviest. and that 17 complete stops were made because of traffic hold-ups.
Similarly, the motorway section between Park Street and Watford Gap— a distance of 55 miles--was covered at an average speed of 42.9 m.p.h., despite the fact that the six-wheeler had to
limp" the last three miles at a speed of about 10 m.p.h. because of the fuel-line fault. The• average speed is even more remarkable _because thick fog patches were encountered at the southern end of MI (a 15vehicle collision occurred that morning because of the fog), and three stops were made in this area.
A record was made of the number of gear changes and brake applications necessitated during these runs, and this showed that on the section out to MbO the brake pedal was applied 36 times, whilst second gear was engaged 19 times, third 26. fourth 28, fifth 19, and overdrive only three times. Overdrive was engaged for 9+ minutes out of an 'overall journey time of 6L minutes, of which seven minutes was spent stationary.
On the M10-M1 section, the brakes were used 13 times at efficiencies of up to 45 per cent.. whilst third, fourth and fifth gears were each engaged four times because of the fog.
Cruising Above 60 m.p.h.
When visibility allowed the Thornycroft to be taken up to its normal speed, it was cruised at just over 60 m.p.h. and on hills it was given its head, At times 67 m.p.h. was reached. The minimum speed on any of the gradients going northwards was 26.5 m.p.h., which shows the advantage of having a 130 b.h.p. engine in a vehicle of this size.
The return run to London was made by using the main fuel tank for the whole journey, and checks showed that 11.05 gallons had been used during the 2-hour 52-minute journey between Sheldon. Birmingham. and Clerkenwell, London. Traffic conditions were light when leaving Birmingham, with the result that the 22.6 miles between Sheldon and the start of the M45 spur were completed in 38 Ininutes (35.6 m.p.h. average speed) with 331 minutes in overdrive.
The 65 miles on M45, M1 and MIO were completed in 1 hour 11 minutes, which gives the notable average speed for that distance of 54.8 m.p.h. This is within 8 m.p.h. of the vehicle's maximum speed, which speaks for itself. The Thornyeroft's ability to worm its way through heavy London evening traffic is shown by the average of 19.4-m.p.h. recorded between Park Street and Clerkenwell.
Out of the total running time between Birmingham and London of 2 hours 52 minutes. the vehicle was on the move for 2 hours 45+ minutes, and overdrive was in use for all but 14 minutes of this. On the last section between Mb O and Clerkenwell. 26 complete stops were made and the brakes were applied 46 times.
Between Sheldon and M45, second, third and fourth gears were each used once, while fifth and overdrive were engaged six times. Overdrive was the only ratio used on the motorway section, but after that second was used 21 times, third 25, fourth 21, fifth 29 and overdrive 13.
The route taken between Clerkenwell and MI0 was the same as that employed during the four-vehicle comparative tests carried out shortly after the opening of the motorway (The Commercial Motor, November 13, 1959), and was by way of King's Cross, Highgate, Finchley and Barnet.
The Mastiff was found to handle extremely well under motorway conditions, and felt completely safe when travelling flat out. Indeed the general handling and quietness of the six-wheeler were far better on the motorway than those of many a private car, and in all respects the design is well suited to highspeed operation.
The flashing indicators are clear and well positioned; the mirrors give a good
range of rearward vision; the wide, wrapround windscreen gives clear forward vision (invaluable in fog; for example); whilst the driving position is as comfortable as one could ask for. The heater was a little disappointing, but the demister portion appeared to be reasonably effective.
The Thornycroft Mastiff 6 x 2 is, in many respects, ahead of its time so far as motorway operation is concerned, and, at present, is outstanding among British heavy vehicles.
It is a good example, however, of what can be produced from a basic design with little modification, and points to what can be expected from other sources in the next few years when motorway operation becomes more generally accepted.
One of the important lessons to be learnt from this Thornycroft vehicle is the emphasis that has been placed on general comfort and controllability essential qualities if motorway working at sustained high speeds is to be both safe and economical.