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 table of steering gear data for the 25 HP model.
| Identifier | ExFiles\Box 106\3\ scan0279 | |
| Date | 5th December 1934 | |
| x5430 Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}24/KW.5.12.34. 25 HP. Steering Gear Data. Type of Steering Gear | R.R. | Marles 15/1 | Marles 17.5/1 | Marles 20.5/1 --- | --- | --- | --- | --- Pendulum Lever Length ins. | Standard 8.250 | 7.600 | 10.15 | 9.50 | 10.15 | 9.50 | 10.15 | 9.50 Mid. Position Box Ratio | 12.5/1 | 12.5/1 | 15/1 | 15/1 | 17.5/1 | 17.5/1 | 20.5/1 | 20.5/1 Lock to Lock Box Ratio | 11.4/1 | 11.4/1 | 14.75/1 | 14.75/1 | 17.2/1 | 17.2/1 | 20/1 | 20/1 Turns of Wheel including comp. of S.S. Tube Springs | 2.43 | 2.60 | 2.54 | - | 3.00 | 3.23 | 3.46 | 3.72 Turns of Wheel without compressing S.S. Tube Springs. | 2.27 | 2.47 | 2.37 | 2.53 | 2.79 | 2.99 | 3.23 | 3.45 Movement of Pend. Lever including comp. of Springs | 76.5° | 82° | 60° | - | 60° | 64.5° | 60° | 64.5° Movement of Pend. Lever without comp. of Springs | 70° | 76.5° | 55.8° | 59.8° | 55.8° | 59.8° | 55.8° | 59.8° Mid. Position Helix Angle | 8.45° | 8.45° | 11.78° | 11.78° | 9.97° | 9.97° | 8.62° | 8.62° Mid Position Ratio Stg. Wheel to Road Wheels | 12.1/1 | 13.15/1 | 11.8/1 | 12.63/1 | 13.8/1 | 14.7/1 | 16.2/1 | 17.3/1 | ||