OPINIONS FROM OTHERS.
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The Editor incites correspondence on all subjects connected with the use of commercial motors. Letters should be on one side of the paper only and typewritten by preference. The right of abbreviation is reserved, and no responsibility for views expressed is accepted.
The Design of the Tractor-lorry.
The Editor, TEE COMMERCIAL MOTOR.
[2182] Sir,—In reply to the letter from Mr. 0. F.•Cleaver in the issue of The Commercial Motor for
May 29th, regarding the position of turntables on tractor-lorries, I cannot quite follow his contention that I increased the lerigth of the body, for it should be evident that this would mean a shorter space fqr cab and engine, which, of course, was not the case. I merely moved the turntable forward, as Mr. Cleaver suggests in the third paragraph of his letter, keeping length of body, tractor and trailer wheelbases exactly the same in both cases.
It could also be shown that, by doing as above, more weight is thrown upon the trailer wheels, and these ought really to be moved farther back (length of body remaining the same), which would further increase the cutting-in angle.
The whole case naturally depends upon length of body and length of tractor and trailer wheelbase. These can, of course, be variously proportioned ; but it is Usual to standardize the tractor wheelbase and make the trailer wheelbase proportional to length of body.
If Mr. Cleaver means moving the middle axle farther back (length of body and position of turntable remaining the same), the cutting-in angle is in this ease reduced, but this is obtained at the expense of increased tractor wheelbase, which alters the steering lock for a given turning. radius. Even in this case, greater width would be required for turning; owing to incres.sed.tractor 'wheelbase, and the three reasons which I gave in my letter in. your issue of May 22nd remain unaltered.—Yours faithfully,
Tractor-lorry or Lorry and Trailer ?
The Editor, THE COMMERCIAL MOTOR.
[2133] Sir,—With reference to letter No. 2178, as a driver of some experience I consider the tractorlorry scores every time. It is much easier to handle than a lorry and trailer, and the brakes on the latter are never too reliable. In fact, trailer manufacturers seem to rely on the brakes of the hauling unit, treating those on their trailers as quite of secondary importance.
As to running costs, I think, if the owner of a
tractor-lorry were to publish a summary of his running costs for a period of not less than three months and Mr. Capper would oblige by getting one of his trailer owners to do this for the same period, it would settle the question as to which is the more economical vehicle to run.
I guess the tractor-lorry is going to prove a winner when it comes to rate reductions.—Yours faithfully, Edmonton. Ex-TRAILER DRIVER.
The Editor. THE COMMERCIAL MOTOR.
[2184] Sir,—There are two letters published in the issues of The Commercial Motor for May 22nd and May 29th, commenting on the letter from me which you kindly printed in your issue of May 15th.
" Tractor-lorry" says that my suggestion that "where there • is no return load for a motor lorry and trailer, the trailer can be left and the motor lorry return alone" is impracticable in most instances, especially where the vehicle has to cover large areas. My reply is that a very small amount of traffic organization of the, railway type enables this arrangement to be carried out with ease, and pays a very high rate of interest on the trouble involved.
For a small contractor it is more difficult, and this is why, here, as elsewhere, combination is essential to enable a clearing-house system to be employed, without which transport cannot be carried on cheaply and—to the contractor—remuneratively. • Such a system is in being, and a small amount of vision would 'enable its application to be so absolutely normal that your correspondent's misgiving would vanish, together with much of the present transport service muddle.
Mr. 0. D. North's letter in The Commercial Motor of May 29th calls for a somewhat detailed reply. I may say at once that the Scammell tractor-lorry pos. sesses features which show that the difficulties of this type of vehicle have been realized and scientifically fought by its designers, but the fuel consumption given by Mr. North of six miles per gallon for a 12-ton load confirms the statement that "with a large vehicle of the six-wheel type, the fuel cost is high" and only needs modification in so far as that it can now be said that this is so even with the best tractor-lorries on the market. With a properly constructed trailer, 12 tons can be carried, with only
10 per cent. more fuel than is required by the motor lorry alone carrying six tons.
Compared with the ordinary consumption with the average lorry and glorified horse-cart-trailer, however, the consumption obtained by this improved Scarnme11 is very good.
Statements one and two made by rrie in my former letter do not appear to be affected by anything said by Mr. North.
With regard to the king-pin and the shocks upon it, I am amazed to hear from Mr. North that these shocks do not exist, and I am afraid I am not con vinced that, by making the king-pin fit—when new— these shocks are eliminated. Their amplitude will
be reduced, but their existence. is, I am afraid, a very real fact. Mr. North's statement that the alternation of tractive effort can be damped out by friction between the turntable plates is, I confess, incomprehensible to me. When Mr. North accuses me a a misieading statement when I say that " with a trailer the hauling power of the motor is utilized," I am sorry, for nothing could be farther from my wishes than to mislead. I only wish to help the Scientific improvement of road transport. Does this, as Mr. North says, suggest that you get " something for nothing "? Is it easier for a man to carry a weight on his shoulder or to haul it on a truck, and, if so_, why are hand trucks, or, for the matter of that, horse-carts, ever used? That is all that is meant, and,I fear Mr. North must have overlooked this simple and fundamental fact, which is, after all, in large part, the justification of the. method adopted by railways, of hauling loaded trains by a locomotive instead of carrying the load on the „cabs of locomotives themselves:
A locomotive, or motor lorry, or horse, or man, will haul much more than it or he can carry—with less effort—if only the vehicle he hauls is properly constructed. Mr. North's remarks about overpowered engine and higher petrol consumption are therefore, beside the point.
In proportion as railway practice is adopted and utilized in road transport, so will economy profit and development of this service be enhanced.—. Yours faithfully, D. 8. CAPPER, M.Tnst.G.E., M.I.Mech.E.,
Director, HAULAGE IMPROVEMENTS AND CONSIRITCTIONS, LTD.
London, IV. C. 2,