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).
Requesting a test to compare petrol consumption between high and low geared back axles.
| Identifier | WestWitteringFiles\C\March1919\ Scan17 | |
| Date | 28th March 1919 | |
| To EH. from R.{Sir Henry Royce} ORIGINAL R2/G28.3.19. X.3056 X.3457 X.3542 RE PETROL CONSUMPTION AND BACK AXLE RATIOS. There is some little doubt as to the effect on petrol consumption between a high geared back axle and a low geared back axle, and I shall be pleased if you can possibly arrange for two cars to be prepared exactly similar, but having back axles having two different values. One would think that the highest and the lowest extremes available would not be too far apart to test, but to find the nature of the curve following this change of back axle ratio, we ought to put in a third or even a fourth ratio, so as to get four values to construct a curve. I know it is quite possible to test on the third or fourth speed of a high geared car, or even standard car which might be done for a preliminary test, but I fear this would scarcely be a fair comparison. I believe that you could get out the old Tourist Trophy four-cylinder car, you would find in the Stores two ratios of back axles, which would give you on the direct drive, two very suitable speeds. I believe the present back axle is one of rather low gear ratio, so this could be tested first. This matter is of the utmost importance to us at the moment, as it depends largely on this whether the fourth speed is necessary on the cars, because if we can obtain approximately the same petrol consumption with a low geared back axle as we can with a high geared back axle over a given road such as we find in England, the low geared axle is so enormously preferable for other reasons of keeping the engine speed up, and allowing ample power without changing gear for traffic, acceleration, and hills. | ||