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 memo discussing the implications of a 3-speed gearbox, synchromesh, and reverse gear design.
| Identifier | ExFiles\Box 94\1\ scan0151 | |
| Date | 5th July 1935 guessed | |
| - 2 - (2) To have only 3 speeds. We attach curves which give some idea of the effect of the use of three speeds on the performance of the car. The bottom gear ratio is .44 which gives the same climbing capacity as the .41 bottom gear of the Cadillac (suggested by Rm{William Robotham - Chief Engineer} as satisfactory). We calculate that fully laden the car will climb 1 in 3.25. (B.M.E.P. 110 axle 4.25, Tyres 14.7" effec. rad. wt 49 plus 8.5 cwt. Trac.Res.80 lbs ton.Transmission eff. .85%.) Figures taken for the Cadillac are - same torque as for the SpectreCodename for Phantom III, axle 4.64, tyres same rad. as for the SpectreCodename for Phantom III, wt 58+8.5 cwts. We have dropped 3rd speed to .71 (from .76). The reduction of speed at maximum r.p.m. is in proportion of course (67/71.5 = 6½%) but the reduction of the effective maximum is only 56/58 = 3.5%). (3) Synchromesh the 1st speed. As we see it the only objection is the train of gears engaged in top gear. With the clutch on the layshaft there would be no extra idling noise, nor any difficulty in operating the synchromesh: The higher the ratio the less the meshing speed in top gear and the lower the speed of the pinion. In this respect we are better now than formerly as we could use a 1st of .4 against .3 in use on our standard cars. There would be no appreciable difference in weight or cost compared with our present box. Presumably if the relay is ultimately required for the Bentley the synchromeshing of 4 speeds must be faced as a Bentley with only 3 would not be very popular we should say. Reverse would be latched out in a way which did not permit of accidental engagement. The Hudson appears to have a slightly projecting lever which is presumably operated by the thumb of the hand which is moving the control lever. | ||