Ors road tests
Page 35
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I have read, with great interest, your article "If it's bad we say so" in CM May 10 1974 and agree that the reports of the tests are most useful to operators who are looking for pointers to help in their purchase of new vehicles.
There are one or two points which I think require some clarification. You must, of course, know the condition of the vehicle before it starts its tests. You do, in fact, use a tape measure to ensure that it conforms dimensionally to the C and U Regulations, but do you also check that the many requirements and standards as listed in the Tester's Manual are met? There have been reports reproduced in the trade papers giving statistics of the number of defects found in new vehicles, eg., FTA recorded 8.68 defects on each new vehicle and over one half had GV9 brake faults, I have noted, in photographs of CM brake tests, one or more wheels on a particular vehicle were showing locked conditions and others were not. I had some correspondence with you about 18 months ago on the question of the correct driving conditions for maximum braking performance, pointing out that this was achieved when the brakes were just not locked, viz, in a practical world by "foot-on, foot-off" driving technique, or, more scientifically, with the aid of Maxaret or similar equipment.
A further case of ensuring that the vehicle is up to standard is illustrated in your trials on the Atkinson Borderer in CM June 23 1972, where the report states that the Atkinson and the Gardner engineers both assessed the vehicle as being in tip-top condition, and yet comments on the subsequent tests indicated that the state of the vehicle at the commencement of the tests was not satisfactory.
There is also the question of whether it is advisable to carry out the tests on a new vehicle, or one that has several thousand miles behind it and hence the "bugs" removed before, it starts, leaving only the things that happen on a day-to-day slog.
In regard to handling, you comment on the general behaviour, as to fatigue in relation to the driver, but I cannot recall any specific remarks on swing, rolling, tendency to jack-knife, etc,: these, of course, mainly in regard to articulated vehicles. It is realized that there are many parameters affecting these features and it would be difficult to be precise.
John-Dickson-Simpson has constructed a safe boundary curve (see Road Way Aug 1973) and a check against this may be quite revealing.
You do quite rightly say that your tests are conducted within limitations but it is suggested that the limitations could be narrowed considerably without much additional effort and provide the operator with a much fuller report.
You will note that my comments are made mainly in the engineering area but I do agree that those generally given are to a very high standard but they are given in the sense of Oliver Twist in merely asking for more.
H. J. WEBB Clevedon [The Technical Editor replies: I agree that maximum retardation is achieved with the wheels almost on the point of locking but in a genuine emergency stop most drivers stand on the brake pedal instinctively without indulging in any "on-off-on" manoeuvres, and our tests simulate real conditions. It would also be difficult to better the full pressure stop as a means of providing comparative figures. From the time point of view we cannot give the road test vehicle a complete DoE check but we have found that most manufacturers ensure that their product is in good condition before we get our hands on it.
The question of whether we use a new vehicle or one with several thousand kilometres on the clock is largely out of our hands as the test truck or bus is supplied by the manufacturer. In fact "brand new" usually means six or seven thousand kilometres on the clock anyway.
Remarks on rolling tendencies can be very misleading as so much. depends on the position of the centre of gravity of the laden vehicle. In the specific case of 32-ton attics, for example, the method of loading varies from manufacturer to manufacturer — some use laden containers, others concrete blocks or sheet steel. Comparing the height of C of G between the container and the sheet steel, for example, one can imagine the variation in handling. We do not recommend a "standard test load" for road tests for the simple reason that we test vehicles for the benefit of the operator and so far as he is concerned there is no such thing as "standard load".]