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).
Comparison of different gearbox ratios and notes on gear manufacturing processes.
| Identifier | ExFiles\Box 137\5\ scan0105 | |
| Date | 25th October 1930 guessed | |
| --3-- To show this approximately - The old 3 speed box would have - Box Ratios Axle Ratios High 1.0 5.0 Second 1.7 8.5 First 3.0 15.0 The spool type four speed box will have - High 1.0 3.8 "Country" Third 1.4 5.3 "City" Second 2.0 7.6 First 3.0 11.4 If a free wheel or Salerni coupling becomes standard for really easy shifting, there will be a reversion to the 3 speed box using ratios somewhat as below - High 1.0 3.8 "Country" Third 1.5 5.7 "City" First 2.5 9.7 In the latter case he considers that it is quite certain that all gears will be helical. He stated that if Derby would care to develop single helical third speeds with dog-clutch shift for either of their boxes, and would send him half a dozen of each size of helical gear with one of the hobs used in cutting them, he would be very pleased to lap these gears to the finish and accuracy indicated by their experience. The only charge would be about $40 per gear-size for the cost of making chills and laps. Note 1 - The thrust of third speed driven gear is habitually taken on a ball-journal bearing. Note 2 - Negotiations with an English Co. to manufacture, use, and sell the gear Process Lapper are approaching completion. Note 3 - Metal Helical timing gears lapped by this process are being developed for the very cheap cars, as a saving over fabric gears or chains. B Maurice Olley | ||