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).
Effects of axle gear and tyre size changes on gearing and transmission efficiency for the 'M' Series Bentley.
| Identifier | ExFiles\Box 83\3\ scan0087 | |
| Date | 12th October 1938 | |
| 200. W/S. Cx.{Major Len W. Cox - Advertising Manager} from Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} Rm{William Robotham - Chief Engineer}/Gry{Shadwell Grylls}1/R.12.10.38. 'M' SERIES BENTLEY. Replying to Cx{Major Len W. Cox - Advertising Manager}12/KW11.10.38., there is nothing wrong in my original memo Rm{William Robotham - Chief Engineer}/Gry{Shadwell Grylls}6/R.7.9.38., the axle gears themselves which are now 10/43 instead of 10/41 would make the car 5% lower geared in direct, except for the fact that the tyres are now 2% larger. This gives a net reduction in axle ratio, or a net increase in engine revs. of 3%. As regards the last part of your memo, the transmission loss due to running in the indirect overdrive gear is so small that we cannot measure it on the chassis dynamometer. This means that the loss will not be more than about 1%. It is of interest that on the ordinary type gear-box the transmission is more efficient in 3rd than in direct because parts of the gearbox are turning slower, and there are less losses due to oil churning. Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} | ||