iNhy not front-wheel drive?
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A PETROL-ENGINED VERSION OF THE USG/ PITT R35 OUTFIT PERFORMED WELL WHEN RECENTLY TESTED BY THE AUTHOR BY R. D. CATER
A M I nst B E August 28 1964 COMMERCIAL J MOTOR published a short article about Bedford R-type conversion carried out intly by Pitt Trailers Ltd. and United Serce Garages of Portsmouth. The vehicle was pipped with a low-level rear end and Pitt 35 suspension which enabled the wheels be retracted so lowering the body to ground vel to facilitate the loading of heavy equipeat.
At the time that article was published the tt/USG R35 as it was known was an [tremely experimental machine which had en designed and built in response to a :quest by the Southern Electricity Board or a vehicle that had a low-loading level at was not articulated. COMMERCIAL IOTOR was able at that time to carry out a Ny short run with the vehicle when, apart DM inefficient braking and a practically on-existent handbrake, it performed exemely well.
Subsequently, the Southern Electricity oard ran the vehicle constantly between outhampton and Birmingham clocking p some 30,000 miles in just over three lonths, during which period no troubles /ere experienced. One of the conditions on thich the makers were promised further rders for the unit was that at the end of this !sting period they would completely strip he transfer box and the front-wheel drive ssembly and check for wear in order to .scertain whether this previously untried lesign would be a practical and serviceable Iroposition. This was duly carried out and, o the complete surprise of everybody inolved, the components stripped in almost perfect condition.
Thus, the ground was laid for further Legotiations with the Electricity Board for he supply of this type of machine which in ervice proved capable of reducing by a considerable amount the handling time involved in the lifting and delivery of substation transformers and drums of cable. Since that time, some 35 vehicles have been produced and are now in service with various Electricity Boards throughout the country, and recently I was given the opportunity to carry out some further testing of a petrolengined version which is due to go into service with the South Western Electricity Board.
Entailing the cutting in half of a standard Bedford R-type four-wheel drive truck at a point just behind the position of the transfer case of that machine and then the joining of this to a shortened version of the Pitt L35 ground-level-loading fork-lift truck carrier, the outfit, although something of a hybrid is nevertheless a very useful machine. And I feel it produced, during the recent tests, an extremely good case for front-wheel drive in commercial vehicles. Obviously, one must be prepared to sacrifice a degree of traction and also be prepared to accept a slightly lowered degree of maneouvrability. The reduction in traction is, however, far less than one would expect and in fact for all normal purposes a vehicle so constructed performs adequately. During the recent tests with the vehicle now constructed to operate with a 5-ton payload as against the 3 tons of the original vehicle, starts were made on gradients slightly steeper than 1 in 5 and even thotigh I was purposely rough with the clutch I found it virtually impossible to make the wheels break with the road surface.
All normal road-going is achieved in much the same manner as with a rear-wheel driven machine, the only difference in feel being found when starting off with the vehicle on full lock when a rather unusually quick move towards the direction in which the wheels are pointing is at first disconcerting. Main roads, country lanes, highways and byways are traversed with no evidence of bad handling characteristics and the only complaint which can be levelled at the vehicle is the very loud and high-pitched whine—well-known to all ex-Servicemen who have travelled long
distances in the war-time Bedford QL troop carrier—which emanates from the transfer box. If anything the suspension of this particular design is better than that of the vehicle in its standard form, the trailing arm design used in the Pitt suspension and the Aeon rubber suspension medium providing smooth and progressive riding characteristics irrespective of the condition of load. An improvement which has been evolved with the assistance of Vauxhall Motors Ltd. is the provision, of standard Bedford R-type hubs and axle tubes for inclusion into the Pitt suspension, so making the outfit 100 per cent Bedford in its running gear equipment. This has obvious advantages with regard to the supply of spare parts. Yet another improvement is the use of the TK Bedford transmission brake in place of a handbrake connected via Bowden cables to the rear wheels on the first version which proved hopelessly inadequate both with regard to braking efficiency and with efficient operation. Completing the road testing, the vehicle was then taken to a location having a grass and clover-covered bank with gradients ranging from 1 in 7 to 1 in 5.25 and concave in formation. The approach to this bank was from a country lane making it impossible to get a flying start and with a gradient meter mounted on the vehicle, and with the banking in a very wet and slippery condition the following results were recorded:— Driving off the road at approximately three miles per hour, the vehicle held its traction until the gradient became 1 in 6. This test was carried out with a fixed throttle setting and holding the steering straight ahead. Leaving the road at the slightly faster speed of nine miles per hour and playing the throttle to achieve the best possible adhesion. the vehicle was coaxed so far as the 1 in 5.25 section of the gradient, at which point no amount of persuasion would keep the wheels gripping and the vehicle subsequently slid all the way back to the bottom of the gradient with the wheels gently turning forward.
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Stding starts were made on sections of 1 in 7 and 1 in 6 on the hill but at 1 in 5.75 was as lost. During all these standing start tests the driver was obliged to deal extremely gently with both the throttle and the clutch, any degree of harshness resulting in immediate wheel-spin. Feeling very satisfied with the performance of the vehicle driving up the hill I turned it about to assess its capabilities in reverse. I was very surprised to find that it would not surmount the 1 in 7 in this direction and no amount of persuasion would get it past this point. On all the gradients used, the handbrake was capable of holding the vehicle but only a very slight movement of the driver in the cab was needed to start the braked front axle sliding on the steepest of the grass slopes. Once this slide was underway the vehicle stayed out of control until a more gentle gradient was reached. Brake tests were carried out in the usual CM manner and the following results proved that the braking system is adequate:— From 30 miles per hour average retardation was 18.4 ft./sec.2 and from 20 miles per hour 13.9 ft./sec.2. This rather lower efficiency from 20 miles per hour points to a vacuum delay in the system although the maximum retardation recorded by the Tapley meter was 8 per cent higher than the maximum recorded on the 30 m.p.h. stops. Tapley meter readings were from 30 miles per hour 66 per cent and from 20 miles per hour 74 per cent. From 20 miles per hour the handbrake produced Tapley meter readings of 31 per cent.
The penalty of a short steering lock— caused by the need to have driving knuckles
and the long wheelbase to impose suf cient loading on the front driving wheels was a turning circle of 71.5 ft. on the le. hand lock and 75 ft. on the right-hand loc Swept circles were 73.7 ft. left-hand at 79 ft. right-hand. A spokesman for the Road Researc Laboratory informed us that the surf-a( used for the tests would produce a co-efficiei w of friction about equivalent to that of stone setts, giving readings of about .17.
It would appear m fro these tests th where a low-level floor line, uninterrupn rear by either a drive shaft or re axle, is requin
front-wheel drive a ve is indeed viable prop. sition, always supposing of course that tl conditions of operation do not pose ar problems with regard to severe gradien having bad surfaces. I feel that while consideration must b given to conditions that will arise durin winter months, particularly in those area which are subjected to long periods of snom bound roads, there is not much to choos between the performance of a vehicle havin this configuration and either a single-driv tandem-bogie machine or a single-tyre, articulated outfit. It has often been said tin the number of hours wasted during a wort ing winter through vehicles being unable t move is so small that vehicles equipped wit double-drive bogies are a liability rather tha an asset. I feel that a machine equipped wit front-wheel drive can be just as useful whe thinking in terms of traction as can any c the many thousands of artics and singlE drive sixand eight-wheelers which have bee used in the past. The axle loadings of the outfit as testel were; front axle 4 tons 9 cwt. 2 qtr. and th rear axle 5 tons dead; making an overai total 9 tons 9 cwt. 2 qtr. The payload carrie. was 5 tons 2 cwt. 2 qtr.