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Page 40
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SIR
TRAFIC NOT A DRAG IN I wish to raise some points on Andrew English's comments on fuel consumption and the aerodynamic characteristics of the Renault T1300, in the recent road test (3 Sept 87).
As a rule-of-thumb, the fuel consumption reduction (%) is no more than half of the drag coefficient (Cd) reduction (%), for a given vehicle at maximum speed. eg 10% Cd reduction gives a maximum consumption reduction of 5%.
The tests were carried out at an average of a little over half max. speed and showed a 45,9% increase over the Ford Transit 120L. If aerodynamic design was a significant factor then firstly, there would not be a considerable difference at this speed and secondly, implies a Cd of approximately twice that of the Transit ie 0,74, which I know is wrong.
I therefore conclude that the reason lies elsewhere, ie the test vehicle, the test method or equipment, or human error. In recent times automotive aerodynamics has become 'popularised' and given both unworthy praise and criticism.
Good aerodynamic design is important for commercial vehicles especially at high, constant speeds over long distances. Many of the socalled drag reducing devices are not quantitively tested and many mis-matched and mis-used.
It is well worth any designer, constructor or operator obtaining qualified unbiased advice at the concept stage, for aerodynamic efficiency and aesthetics. Trevor Haynes MSc BSc Aerodynamicist Birmingham
PAICE, SET AND MATCH MI We were interested to read the letter from Mr RA Paice in your issue of 8 October. Our new 'B' type tender does bear an external resemblance to the old Chubb Pacesetter. We
were in fact very closely involved with the Pacesetter, which was built on our specially designed rear-engined 'Scorpio' chassis.
However, probably because of its price and because it was too revolutionary a departure from accepted practice, the Pacesetter was unfortunately not the success that both we and Chubb had hoped it would be.
Having taken a fresh look at the Brigades' requirements we believe we now have a 'B' type tender that meets their needs, at a price which is competitive with the standard product. RW Boughton Company Secretary Reynolds Boughton (Devon) Ltd.
EMOTIVE MI "Motorway Accidents" and "Speed Limits" are emotive words to the general public, especially when used in combination. So I can well under
stand Mr Shennan (Dear Sir, CM 30 Sept).
In fact, speed limits are a nonsense: they take account only of road type, whereas the maximum safe speed will depend on a whole host of factors which can change dramatically within the space of a few seconds.
Car drivers who allow themselves to be "tailgated" should ask themselves whether they would accept "handbrake" performance should they need to stop suddenly, because that is what they will get as the vehicles behind pile successfively into them.
Contraflows are not dangerous. Actually, they are safer than a two-way road with double