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 dynamo speed on a 20 HP vehicle based on tyre size, axle and gear ratios.
| Identifier | ExFiles\Box 39\2\ Scan010 | |
| Date | 28th April 1917 | |
| R.R. 235A (500 T) (S.D. 408. 28-4-17.) Bin. 2/156/13. X. 3533 To EFC. from Da.{Bernard Day - Chassis Design} June X.3481 X.3533 ✔ - 20 H.P. DYNAMO SPEED Tyre - 820 x 120 = 32.25 inches diameter. Back Axle Ratio = 4.1 Gear Box ratio - Top - 1. 2nd.- .657 1st.- .392 Tyre does .0016 miles per rev. } - on top. or .0004 - miles per engine rev } On top - 41.7 R.P.M. on 2nd.- 63.5 R.P.M. on 1st.-106.3 R.P.M. As ratio of dynamo to engine is 1.6 at 1 M.P.H. dynamo does :- On top - 66.8 R.P.M. " 2nd.-101.7 R.P.M. " 1st. 170.2 R.P.M. Da.{Bernard Day - Chassis Design} | ||