Explaining the calculation of engine r.p.m. figures based on various tyre rolling circle measurements for an attached chart.
| Identifier | ExFiles\Box 156\4\ scan0133 | |
| Date | 27th September 1943 | |
| 1330 To. Wym {G. Harold Whyman - Experimental Manager} /CD. from Ev {Ivan Evernden - coachwork} /JD. {J. Draper - Frames} c. to. Wym {G. Harold Whyman - Experimental Manager} c. to. Rm. {William Robotham - Chief Engineer} c. to. Ev. {Ivan Evernden - coachwork} Chassis Performance Handwritten note: Coymn Can I have these figures on my board. Also 30 GVI & 11 BVI Rm {William Robotham - Chief Engineer} - Car Engine R.P.M. at 60 miles per hour. We have taken out engine r.p.m. figures for the cars in the garage when they are travelling at 60 miles per hour, based on the back axle ratio and the rolling circle data given us by yourself. This information is given on the attached chart. Column 4 on the chart shows the measured rolling circle supplied by the garage. Column 5 shows the same rolling circle taken from the standard tyre charts. Column 6 shows the rolling circle at 30 m.p.h. taken from the standard tyre charts. Column 7 shows the estimated rolling circle at 60 m.p.h. When viewing these columns it will be seen that the rolling circle of the tyre is greater when the vehicle is moving at speed, to that just being rolled along the garage floor. Columns 8, 9, 10, show the engine r.p.m. at 60 miles per hour. Column 8 is using the garage measured rolling circle to obtain the figure; Column 9 is using the estimated rolling circle to obtain the figure. It is suggested that column 10 will probably be the most accurate figure to use when the car is travelling at 60 miles per hour as it is an average between columns 8 and 9. Handwritten note: These are OK Wym {G. Harold Whyman - Experimental Manager} /CEF Ev {Ivan Evernden - coachwork} /JD. {J. Draper - Frames} | ||
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).