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 memorandum detailing the design considerations and performance of the Myth rear suspension system.
| Identifier | ExFiles\Box 110\3\ scan0011 | |
| Date | 8th October 1940 | |
| 1080 To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/GB. Copy to Ev.{Ivan Evernden - coachwork} Rm{William Robotham - Chief Engineer}/CLM.{D. D. Clapham} Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} 746 Rm{William Robotham - Chief Engineer}/GB.2/ET.8.10.40. MYTH REAR SUSPENSION ------------------ Here are some details concerning the Myth rear suspension. This suspension was to have consisted of a 44" spring and a tension shackle. A spring position was chosen by Rm{William Robotham - Chief Engineer}/GB. which gave a reasonable amount of understeer (just over 4%) with two passengers and which kept the rear eye near the frame. To guard against the suspension having undesirable rate characteristics a number of graphs were constructed showing load, rate and deflection curves for various shackle lengths and offsets. Figure 1 shows such a set of curves for a fairly normal suspension (2 1/2" tension shackle with 1/2" offset). This suspension does not increase in rate as passengers are added. On a small car where the passengers form a relatively large part of the total sprung load, this will result in a very noticeable change in the ride. This suspension cannot therefore be uniformly good whatever the number of passengers carried. If the shackle offset is changed to give a rising rate around the normal ride position, the rate rise will be too rapid as the bump position is approached. A larger shackle is therefore very desirable. By trial and error methods a suspension was chosen which was considered to be a good compromise. See fig. 2. A 4.5" shackle was used to get this. At a conference held at Park Leys on 2.10.40, Ev.{Ivan Evernden - coachwork} stated that the above shackle would not give sufficient ground clearance and that propeller shaft pumping would be more than was liked. A compression shackle was therefore indicated together with a different spring camber. Fig. 3 shows curves for a 2 1/2" compression shackle. There is a very considerable drop in rate as bump is approached. This is undesirable for obvious reasons. A 5" compression shackle with a fairly large offset and the new spring camber gives the curves shown in fig. 4. These curves show only a small change in the virtual deflection over the possible load range and are considered to be quite satisfactory. Rm{William Robotham - Chief Engineer}/GB. | ||