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 specifications for two different steering gear systems, the Standard 20/25 and the 20/25 Marles.
| Identifier | ExFiles\Box 28\3\ Scan120 | |
| Date | 21th February 1935 guessed | |
| Standard 20/25. 20/25 Marles. as tested. Pendulum lever length. 8.250 10.15. Pendulum lever angles. 65º 52½º Lock angle (o/s wheel). 65½º 65½º Ratio between lock and pendulum lever. .997 .810. Steering column ratio = 1.4 x 2π / .700 = 12.55 2.25 x 2π / .665 = 21.3 Overall ratio. = 12.55 x .997 = 12.50 .810 x 21.3 = 17.2 Turns from lock to lock 2.25 3.10 Helix angle 8º27' 8º37' (at centre of worm). Lead .700 .665 Radius of rocker arm 1.400 2.25 (equivalent) | ||