From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'THE AUTOCAR' detailing comparative tests between Palmer cord tyres and standard canvas tyres at Brooklands.
| Identifier | ExFiles\Box 1\7\ B001_X15 20 46 50 59-page131 | |
| Date | 16th January 1915 | |
| THE AUTOCAR, January 16th, 1915. 71 Comparative Tyre Tests. The Respective Merits of Cord and Canvas Covers. NOT long ago the Palmer Tyre, Ltd., carried out some tests on Brooklands with a view to making direct comparisons between the behaviour of their own Palmer cord tyres and some tyres of another well-known make. Of course, the basic difference between the construction of a Palmer cord tyre and the ordinary cover is in the casing alone; instead of superposed layers of canvas being used as the containing envelope for the air tube, Palmer tyres are made up by crossed layers of cord, each cord being insulated from the next by a rubber skin. For this construction, the Palmer Co. have made strong claims on the score of durability, and the tyres have been on the market so many years now that these claims have been publicly proved and no one questions the remarkable longevity of the tyres. On the other hand, those who have admitted this have sometimes questioned their resilience and have certainly not regarded them as having qualities which tend towards economy in petrol consumption. The extensive use of them in racing and record-breaking has been more often regarded as a tribute to their durability than to their actual tractive efficiency, though the Palmer people themselves have always claimed that their tyres were fast, and, obviously, to be fast they must be tractively efficient, or, in other words, the minimum amount of power must be wasted in the tyres. [Chart 1: COMPARATIVE PETROL CONSUMPTION TESTS AT BROOKLANDS. MILES RUN ON ONE GALLON] TYRES: 880 x 120 m/m, M.P.G.: 18 Mls 897 Yds. TYRES: 880 x 120 m/m PALMERS, M.P.G.: 20 Mls 781 Yds. [Chart 2: COMPARATIVE SPEED TESTS AT BROOKLANDS. MILES RUN IN AN HOUR (SET THROTTLE)] TYRES: 880 x 120 m/m, MILES RUN: 31.68 Mls. TYRES: 880 x 120 m/m PALMERS, MILES RUN: 33.89 Mls. [Chart 3: COMPARATIVE COASTING TESTS AT BROOKLANDS. DISTANCE RUN IN FEET] TYRES: 880 x 120 m/m, MAX RUN IN FEET: 1118 Ft., SPEED: 21½ TYRES: 880 x 120 m/m PALMERS, MAX RUN IN FEET: 1746 Ft., SPEED: 24½ Three diagrams showing comparative tests of petrol consumption, speed, and coasting as affected by the employment of ordinary canvas tyres and Palmer cord tyres. In each case the axle loads were the same, namely, 20 cwt. front and 24 cwt. back. The air pressures used were 60 lb. per square inch front and 72 lb. per square inch back. Above we give a graphic table showing the results of the tests made by the Palmer officials on Brooklands. These comparative graphs are the mean of a large number of trials made with both the Palmer and the ordinary canvas tyres; the ordinary tyres are shown with a full black line and the Palmer results with a grey line. In each test the front tyres were inflated to 60 lb. and the back to 72 lb., the car weighing 2 tons 4 cwt., 1 ton 4 cwt. of this being on the back axle. The tyres in each case were 880 mm. x 120 mm. It will be seen that on petrol consumption the ordinary tyres covered 18 miles 897 yards to the gallon, while the Palmers covered 20 miles 781 yards, or very nearly two miles more. In the speed tests the throttle was fixed at a given position to provide a speed of round about thirty miles an hour; with the ordinary tyres 31.68 miles were covered in the hour, with the Palmer tyres 33.89 miles. Lastly, coasting tests were made, and in some respects these are even more striking than the other two. The car was released from the mouth at the end of the finishing straight, not from the banking, and allowed to run till it stopped. At this point the gradient is 1 in 12 and about 520 feet long; owing to the height of the banking above the mouth one scarcely recognises how much the straight is inclined so as to bring down the speed of the cars finishing in races, as, of course, they run in the opposite direction. From a standing start the ordinary tyres coasted 1,118 feet, attaining a maximum of 21½ miles an hour, while the Palmer cord tyres coasted 1,746 feet, reaching a maximum of 24½ miles an hour. Quite apart from any other consideration, it is most interesting to observe the consistency of these tests, any one of which would indicate the results of the other two. That is to say, whether a car with its tyres changed runs more miles to the gallon, goes faster, or coasts further, it is obvious that the tyre change which gives this improvement must result in the other two advantages, because they all mean the same thing, and that is that less power is absorbed by the tyres. The tests, we regret to say, were not conducted by the R.A.C., and doubtless for that reason the Palmer Co. offer facilities to motorists to repeat them themselves. We presume the R.A.C. would not conduct them, as they necessitated comparative tests between two different makes of tyres, just as the Victor tests necessitated comparative tests between four makes, and which the Club declined to conduct. No doubt the Club has its reasons for this attitude, but we have always regretted it, as it tends to (1) unofficial trials, or (2) the motor world being the poorer by lack of valuable comparative data. [Handwritten Annotation in left margin]: X2 | ||