OPINIONS and Q UERIES INCONSISTENCIES IN TYRE OVERALL DIAMETERS A READ
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with mixed feelings the leading article, "Why Do 'Tyre Overall Diameters Vary?" in your issue dated October 18.
Before attempting to shed some light on this controversial matter, I would like to draw attention to the mistake made in attributing an overall diameter of 4 ft. 01 in. to 34 by 7 tyres. Actually, they vary between 36 and 37 ins., 4 ft, being applicable to 1400/20 tyres, the largest in general road use in this country!
In the article a great deal is made of a difference of in. in overall diameter in the same size tyre, but from different manufacturers.
Now, what does this # in. really mean? I agree it represents approximately. 2 ins, in total circumference. On a 34 by 7 tyre, 2 ins. = approximately 11 per cent. of the circumference. 2 ins. = approximately, 1 rev, in every 56. 2 ins. — approximately, 10 revs, per mile. On a 1400/20 tyres: 2 ins. = approximately l per cent. of the circumference. 2 ins. = approximately, 1 rev, in every 75. 1 ins. = approximately, 6 revs, per mile.
In other words, one half-shaft, in these two cases, completes, in one mile on a straight road, 10 and 6 more revs, than the other corresponding half-shaft. I submit that these can be disregarded, and that the operator whose axle ran so hot should look to other causes than I in. difference in overall diameter. Actually, overall diameter has very little meaning except for clearance purposes to body, etc.
The figures which form the true comparison are the radii of tyres under load deflection. The amount of deflection can vary quite appreciably in different makes, e.g.: 1400/20, Make A = 47.75 in. overall diameter. Make B = 48.80 in. overall diameter..
Deflected under load, Make A = 22.75 in. radius. Make B = 22.80 in. radius.
Another point which must be considered is that of the varying depth of tread pattern as a tyre wears. From new tyre to smooth tyre can produce up to 1 in. difference in overall diameter in the same size tyre of the same manufacture.
What it all boils down to, is that the understanding of tyres and their application to vehicles is just as much a science as any engineering practice.
W. L. BARNES.
TYRES AND THE WAR THE booklet recently issued by the Tyre Maaufacturers Conference, giving a review of the achievements of the British tyre industry during the war year's, contains a wealth of information which offers fascinating reading, and confirms the, fact that British tyre manufacturers dealt with magnificent success with problems of the greatest difficulty and• complexity_ The booklet, however, is confined entirely to the work undertaken by the new-tyre .manufacturers,
The impression :left upon the reader of the booklet must be that the new-tyre makers were entirely responsible for everything that was devised or developed in the fight to economize in the use of rubber and other materials required for tyres, and that not only in the matter of new tyres, but also in that of retreading tyres, the Tyre Manufacturers' Conference was the prime mover in every instance in the saving of the tyres we had. Such, however, is far from the case. The British tyre retreaders, as a body, threw all their energies into this essential and vital work, and it was almost entirely due to the persistence and enterprise of one of their number, Tyresoles, Ltd,, that the retreading of tyres by the British Army itself was initiated and developed. Furthermore, as early as 1939, Tyresoles, Ltd., installed a retreading plant at Henlow for the Air Ministry, where throughout the war thousands of tyres required for Royal Air Force vehicles were reconditioned.
On page 14 of its booklet the Tyre Manufacturers' Conference refers to the establishment of retreading and repairing units behind the lines in the different theatres of war, completely ignoring the fact that it was Tyresoles, Ltd., which supplied the retreading equipment for the earlier of these plants.
The truth of the matter is that but for the strongest advocacy by Tyresoles, Ltd., of the vital necessity of having tyre-retreading plants right behind the Fighting Forces, and the courage of certain officers who persisted in advocating the schemes put forward by this company, despite violent opposition from many who should have known better, it is doubtful if a comprehensive programme of tyre recovering and reconditioning in the war zones would ever have come into being, or it would have come so late as to be virtually useless.
Many thousands of Army tyres were reconditioned in the plants supplied by Tyresoles, Ltd., the first of which was installed in 1941. Detailed plans for a mobile retreading plant for theArmy were prepared by us early in 1940, so that here, again, some credit is surely due to the British retreaders, and should not be taken entirely by their more powerful brothers.
There is one other point we would like to make, as here, again, the inference is that only the members of the Tyre Manufacturers' Conference were involved. On page 15 there is a reference to the training of a total of 5,000 R.A.F. personnel in tyre maintenance. Tyresoles, Ltd., operated a series of similar schools from September, 1942, which ran for nearly three years, during which time 4,170 officers and other ranks passed through, including a large number of American Service men; we believe other retreaders also played their part in this valuable work. F. C. PALMER Wembley, London. (For Tyresoles, Ltd.).
WAS THIS RATE. CUTTINGS IT is deplorable, but none the less a tragic fact, that our 'industry is returning to the old system of rate-cutting.
We received an inquiry to carry 4 tons 16. cwt. of steelwork from the Midlands to Beverley, Yorkshire. (Point of collection to point of delivery 155 miles.) Our quotation was £2 5s.. perton. Our clients are getting the work done at over £4 per load less than our quotation. I would be glad if there is anyone on the staff of "The Commercial Motor " or in the road-haulage indristry in the United Kingdom Who can prove to me that this is an economic. rate.
Is it not time that. some system was evolved inside the industry whereby firms, indulging in this pernicious system could be publicly black-listed?
G. A. TAYI,OR, Proprietor, Dudley. (FOr G. A. Taylor's Transport}.