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).
Cranking rig tests performed on Myth rear springs supplied by Toledo Woodhead.
| Identifier | ExFiles\Box 154a\2\ scan0356 | |
| Date | 1st July 1941 | |
| To: Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/GB. c. Rm{William Robotham - Chief Engineer}/Clm.{D. D. Clapham} Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} CRANKING RIG TESTS ON MYTH REAR SPRINGS BY TOLEDO WOODHEAD One pair of T.W. rear springs have been put by for a Myth chassis. One of the other pair has been rig tested. On rig tests of car rear springs at Vauxhall, the stroke of 7½" was divided equally on either side of the four passenger load position. On rig tests of Bedford truck rear springs, this procedure was far from being successful. The springs have a dual rate and leaves broke in all sorts of positions where breaks did not occur on the road. Bedford springs are now tested from the unloaded vehicle position to the full bump. Neither of these methods is considered to be suitable for the Myth rear springs where we have a private car with a considerable rise in the suspension rate with increase in load. For the first Myth spring, the stroke was maintained at 7½" and it was divided so that the work done on the spring was equal on either side of the four passenger load position. This was done by measurement on the graph of a test on a T.W. spring with a shackle (See Rm{William Robotham - Chief Engineer}/GB.12/ET. 24.4.41) which showed that the centre of the spring should go 3.2" towards bump and 4.3" towards rebound from the four passenger load position. The suspension load for four passengers is 810 lb. per side. Owing to the shackle effect, the corresponding spring load is 827 lb. With this stroke arrangement, the relationship between rig life and road life should be about the same for the Vauxhall & Myth rear spring tests. Vauxhall 10 rear springs have a life of 30,000 to 60,000 cycles. They are not a cause of trouble and few spares are sold. As a further guide as to the life required, a memo from Olley is reproduced here :- LEAF SPRING TESTS 25th Nov.1937. BUMP RIG AND CRANKING RIG "In response to a cable Cadillac advises that leaf spring "expectancy" on cranking rig is 100,000 cycles of 8" stroke or over half million of 4" stroke. -Continued- | ||