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).
Specifications and suitability of rear road springs for the Bentley 50.
| Identifier | ExFiles\Box 112\1\ scan0072 | |
| Date | 7th January 1938 | |
| To By... from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} c. to Ba. c. to RM.{William Robotham - Chief Engineer} c. to Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/Les.{Ivan A. Leslie} 104H GRY{Shadwell Grylls} 8406. Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}1/N.7.1.38. Rear Road Springs for Bentley 50. ------------------------- There seems no reason why the present rear spring length of 50" of B.III should not be adequate for Bentley 50, even if very soft springs be required for this latter car. For a given length of spring the maximum stress range is decided purely by the leaf thickness and the deflection range, and if the latter is limited, then the spring stiffness will make no difference to the stress range of the top leaf. If we take the recommended stress range of Firth's letter reference WHH/MW. of the 30.12.37, of 30 tons/in² plus and minus, i.e. arrange the main spring leaf to have equal movements up and down from its own neutral position, as suggested in BY.15/G.{Mr Griffiths - Chief Accountant / Mr Gnapp} of 22.12.37, and assume a maximum range of movement of 10", which is within 0.25" of that employed on Phantom III we can still have a main leaf thickness of 0.292" which is more than that of the present Bentley rear springs. Actually the axle movement at the rear of B.III is limited to approximately 7.375" by the frame on one hand and the exhaust pipe on the other, and this movement would allow a main leaf thickness of 0.325" without exceeding the stress range of the present 25/30 rear spring leaf, the main spring leaf then being arranged to be unstressed in the controlled rebound position. It is interesting to note that Woodhead's, when I visited them recently, said that they work to a scrag stress of 68½ tons per sq.inch, for their standard production, which corresponds to approximately 11.4" of movement of a 50" spring with a main leaf thickness of .292" and it would be possible to get a 7.00 static deflection with a stress of 42 tons per sq.inch. i.e. with their suggested figure of rather more than half the scrag stress, this being a low-rated spring. It might be interesting to find their reaction to such a suggestion. Cont'd..... | ||