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).
Calculations for the 20 HP chassis gears, including speeds, tyre dimensions and various ratios.
| Identifier | ExFiles\Box 49\1\ Scan076 | |
| Date | 12th June 1919 | |
| X 3493.✓ 12.6.19. X.3481 / X 3501. 20 H.P. CHASSIS GEARS Tyres 820 x 120 i.e. 32.250 inches dia. Distance traversed per rev. = 101.2 inches. = 101.2 / (1760 x 36) miles per rev Back axle ratio = 15/60 = 1/4 = .00160miles per rev. of road wheel. .. 4 revsof engine give .00160 miles ( on top gear ) or 1 rev of engine gives .00040 miles ( ditto ) .. at engine speed of 1000 R.P.M. car does .4 miles per min. = 24 miles per hour. on top gear. Ratio of 2nd. gear is .657 1st. gear is .392 .. M.P.H. at 1000 R.P.M. on top gear is 24 on 2nd. gear is 15.78 on 1st gear is 9.4 Ratio between dynamo and crankshaft speed is 40/25 = 1.6 at 1 M.P.H. engine does 1000/.4 R.P.M. = 41.7 R.P.M. on top gr {George Ratcliffe} + 63.5 R.P.M. on 2nd. gear + 106.3 R.P.M. on 3rd. gear and dynamo does at same cor. speed. 66.8 R.P.M. on top gear. 101.7 R.P.M. on 2nd. gear. 170.2 R.P.M. on 3rd. gear. | ||