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).
Test data for a Firths rear road spring, showing weights applied and released.
| Identifier | ExFiles\Box 52\2\ Scan075 | |
| Date | 16th March 1923 | |
| Mr. Hives. from GWH. {George W. Hancock - Head Chateauroux} X4429 16.3.23. REAR ROAD SPRING - FIRTHS. 2200 lbs. 10 plates. | | Weight applied. | Weight released. | |:--- |:--- |:--- | | ½ | 518 | 441 | | 1 | 847 | 882 | | 1½ | 1323 | 1183 | | 2 | 1708 | 1680 | | 2½ (flat camber) | 2114 | 1804 | | 3 | 2527 | 2331 | | 3½ | 2821 | 2828 | | 4 | 3381 | 3115 | | 4½ | 3850 | 3619 | | 5 | 4270 | 3920 | | 5½ | 4604 | | leaves dry. | ||