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).
Suspension design, specifically spring length, stiffness, and damping for new car models.
| Identifier | ExFiles\Box 71\2\ scan0144 | |
| Date | 25th April 1926 guessed | |
| -2- Contd. these are now demanding to be longer, so that we are trying the new models EAC. 1 & 7 with 48" and 45" springs, and even should we find some distinct modification of the front axle system I believe we must as soon as possible increase the spring length, the great advantage being that the longer the spring the less the tendency for the axle to turn over by the brake and steering reactions. I conclude that it is inversely proportionate to the length but it may be more or less. DA{Bernard Day - Chassis Design} will correct this statement. To make the best of the present cars we decided on a compromise of 12½% increase in pre-front wheel brake stiffness. OY. says we have been deceived under actual working conditions and have been fitting 35/50% increased stiffness. I have wired to check this at Derby; it can be done two ways - i.e. by the natural period of vertical vibration or by carefully weighing the load carried by the spring at normal, and then adding and reducing the load for 1" or 2" each side of normal. I have suggested 30 to 32% per inch but we must first see that the springs are correctly and actually loaded with the weight they will be asked to carry on the car, so that there are two items to be right (1) Are the springs right for the load ? (2) What is the stiffness under exact working conditions and is it the least that is practical for other well known reasons ? Ordinary well greased springs do not seem to have too much internal friction to be detrimental - i.e. greater than the minimum permissible damping (my tests here confirm). I am convinced that we must have still more effective damping in the least harmful form (which we have arranged in the hydraulic dampers) but that my own personal experience shews that it would be fatal to turn out cars insufficiently damped. They are dangerous beyond words as well as most uncomfortable, at even slow speeds (20/30 MPH) on bad roads, and I consider that our greatest mistake in the past was to try to do without effective dampers on the back of the cars. We were going right with hydraulic dampers (1908) and fortunately always fitted dampers to steady the front of the car, but external influence made us endeavour to eliminate all damping in the back, even in the springs. We must not again be tempted to have insufficient damping on either axle. Contd. | ||