SOME POINTS CONCERNING THE SEDDON TRACTOR UNIT
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YOUR road-test report of the Seddon tractor with
two-speed axle and semi-trailer, published in your issue dated February 6, makes one wonder if the extra high ratio is worth while, as the fuel consumption does not appear to be much reduced.
T venture to suggest that the vehicle, as tested, was over-geared, and considerably better results might have been obtained had the axle ratios been lowered by 20 per cent.
It is the writer's opinion that some of the overall gear ratios are so close to one another as to be hardly worth the extra' mechanical complication. Also, I believe that 70 b.h.p. is barely enough power for a gross weight of over: .14 tons, but, correctly geared, such a vehicle should give a ftiel return of 13-14 m.p.g.
I suggest that a single-speed axle of 810-1 ratio with a five-speed gearbox having ratios of 7, 4.5, 2.5, 1.7 and 1 to 1 would give much better results and would certainly increase road performance whilst bettering the fuel consumption. J. L. G BREWSIF.R.
(For J. Brewster and Co. (Transport
Newcastle-upon-Tyne, 4. Engineers), Ltd.) [We took this matter up with Seddon Motors, Ltd., and Mr. R. H. Seddon has written to the effect that this is a vast subject, and to do it justice would require a reply of considerable length. It may be sufficient, however, to say that he knows of no set of gear ratios which would be ideal for every condition of service, and in the interests of economy a compromise has to be arrived at. The company believes that in the gear. ratios of the tractor unit tested, it has arrived at .a reasonably good compromise in the light of its experience to date. It is almost certain that if a single-speed axle ratio of 8 to I were to be adopted there would be complaints that the vehicle was too slow, and it must be remembered in this connection that most vehicles operate over considerable distances at less than their maximum load capacity.-ED.]