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).
Technical analysis comparing the Bentley III gearbox and overdrive with its potential application on the Phantom.
| Identifier | ExFiles\Box 99\4\ scan0282 | |
| Date | 6th May 1937 | |
| COPY. W/S. Cx.{Major Len W. Cox - Advertising Manager} E/HGY.1/HP.6.5.37. Bentley III Gearbox. In reply to Cx.{Major Len W. Cox - Advertising Manager}8/KW.3.5.37 I consider that although from a technical point of view, my remarks concerning the Bentley apply with equal force to the Phantom, owing to the difference in type of car and the manner in which the cars are likely to be driven, there is more to be said in favour of the over-drive on the Phantom from the customers point of view. I am assuming that there is an appreciable increase of silence and smoothness when in the over-drive, and that the over-drive itself is sufficiently silent. I have not yet had any personal experience of the over-drive. Dealing in detail with the points made in my memo on the Bentley as regards their application to the Phantom:- (1) The average driver of the Phantom is presumed to make less use of the maximum acceleration of which the car is capable when the gears are used fully. Therefore, even if the over-drive ratio is not much used, there will not be the same resentment about the lower 3rd speed and the loss of the 2nd speed as would occur with the Bentley driver, to whom a fierce acceleration is an essential requirement when occasion demands. (2) It is presumed that a change into 3rd is much less frequently made on a Phantom because the acceleration on direct drive is enough for ordinary comfortable travel. It is also unlikely that high speeds will be required from 3rd to the same extent as on the Bentley. (3) The proposed ratio for the gear below direct drive on the over-drive box is .68. This should enable the car when loaded to 59 cwts to climb not more than 1 in 5 continuously. Therefore, 1st speed may be required on hills such as Porlock and Countisbury and on some of the Alpine Passes when laden to the weight given. For some drivers this may prove to be rather disconcerting as it is impossible to change into the unsynchronised first speed without double declutching, except when the car is almost at rest. The same applies to the present 1st speed but with a four speed box 1st speed is only used for starting. | ||