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).
Technical memo detailing modifications and calculations for the Myth rear springs.
| Identifier | ExFiles\Box 110\3\ scan0036 | |
| Date | 13th January 1941 | |
| To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/GB. Copy to Ev.{Ivan Evernden - coachwork} Rm{William Robotham - Chief Engineer}/HH. Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} Rm{William Robotham - Chief Engineer}/Clm.{D. D. Clapham} Ev{Ivan Evernden - coachwork}/DB.{Donald Bastow - Suspensions} MYTH REAR SPRINGS. Some modifications are necessary to the Myth rear springs shown in PL.370. Since these were designed, the car weight has increased from 20 to 22 cwt. and we have changed from a tension shackle to a compression shackle with a different offset. The following assumptions have been made to arrive at the new sprung load. Kerb weight of car 22 cwt. Position of C.G. 44" ahead of rear axle Rear axle weight (Kerb) 55/99 x 22 cwt. = 1369 lb. Rear axle weight due to " " 4 passengers 420 lb. " " due to luggage 72 lb. Total rear axle weight 1861 lb. Rear unsprung weight 240 lb. Sprung weight - total 1621 " " - per side 810 Spring camber at full load is - .31" The attached graph shows the curves for load, rate and virtual deflection. The bump stop should be lengthened so that it makes contact at 2" from the full load position in order to keep the rate rising all the way to the bump position. Suspension and spring loads and rates are as follows Suspension load per side 810 lb. Suspension rate at full load 810/5 = 162 lb/inch. Spring rate when flat 132 lb/inch. Spring load at full load position 827 lb. " " " no camber 788 | ||