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 data for various types of 25 HP steering gear.
| Identifier | ExFiles\Box 28\3\ Scan080 | |
| Date | 7th January 1935 | |
| Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}12/KW.7.1.35. 25 HP. STEERING GEAR DATA. | Type of Steering Gear. | R.R. | | Marles 15/1 | | Marles 17.5/1 | | Marles 20.5/1 | | | Standard | | | | | | | | | Pendulum Lever Length - ins. | 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 | 11.9/1 | 11.8/1 | 14.75/1 | 14.75/1 | 17.2/1 | 17.2/1 | 20/1 | 20/1 | | Turns of Wheels including comp. of S.S. Tubes Springs. | 2.31 | 2.50 | 2.36 | - | 2.80 | 2.98 | 3.23 | 3.43 | | Turns of Wheel without comp. | 2.15 | 2.31 | 2.20 | 2.34 | 2.58 | 2.77 | 2.98 | 3.20 | | S.S. Tube Springs Movement of Pend. Lever including comp. of Springs. | 70.5° | 77° | 56° | - | 56° | 59.5° | 56° | 59.5° | | Movement of Pend. Lever without comp. of Springs. | 65° | 70.5° | 51.5° | 55.5° | 51.5° | 55.5° | 51.5° | 55.5° | | 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 | | ||