Comparison of three different tires with varying sizes and tread pitch designs.
| Identifier | ExFiles\Box 157\2\ scan0224 | |
| Date | 17th January 1938 guessed | |
| 7 x 18 C VARIABLE PITCH 7 x 18 XI PLAIN 7.5 x 18 C NON VARIABLE PITCH | ||
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).