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).
Gear and axle ratios for the Junior Gearbox on the Rippletto and Myth class cars.
| Identifier | ExFiles\Box 136\2\ scan0222 | |
| Date | 8th March 1940 | |
| 1153. To Rm.{William Robotham - Chief Engineer} from Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} c. to Rm{William Robotham - Chief Engineer}/CPS. c. to Rm{William Robotham - Chief Engineer}/PD. c. to Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} c. to Ev{Ivan Evernden - coachwork}/Tarlton. Ev.{Ivan Evernden - coachwork}9/JH.8.3.40. Junior Gearbox. Attached herewith is a chart of particulars of cars of the Rippletto and Myth Class, giving weights, gear ratios, axle ratios etc. It would appear that in general a bottom gear ratio of .240 is as low as we need go in our Junior box, even though we may use it on Rippletto as well as Myth. The axle ratio ordered on the Salisbury axle for Rippletto is 4.56 to 1, giving 70.7 m.p.h. at 4000 r.p.m. and 6 x 16 tyres. We had projected the Myth with 16 x 5.5 wheels and a rear axle ratio of 4.88 to 1 which gives a top speed of 71.4 m.p.h. at 4000 r.p.m. This would appear to be a rather higher ratio than that used on competitive cars of about the same power and weight. We suggest we may wish to use the alternative ratio given by Salisbury on their smallest axles i.e. 5.38 to 1. This would give 64.800 m.p.h. at 4.500 r.p.m. Ev.{Ivan Evernden - coachwork} | ||