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).
Study on spring suspension frequency related to deflection and passenger comfort.
| Identifier | ExFiles\Box 43\2\ Scan085 | |
| Date | 18th December 1925 | |
| Oy4-E-121825 -2- December 18, 1925. We have all along worked on the assumption that the frequency of the spring suspension depended on its deflection and was independent of the load or rating (i.e. a baby carriage and a 7 ton truck which deflect their springs the same amount will bounce at the same speed). The assumption that the frequency is the same as the swinging frequency of a simple pendulum of length equal to the deflection - (or frequency per sec. = 1/2Π * sqrt(32.2/deflection)) -- we find approximately correct for either end of the car, except for the stiffening effect of leaf friction, (and of clipping the springs, referred to later) which always speeds up the bouncing a little. We have made the following table:- Deflection Theoretical Observed frequency inches frequency per min. with normally lubricated springs. Front springs 1" 188 --- 2" 133 --- 3" 108 120 - 140 3 1/2" 100 115 - 120 4" 94 --- 5" 84 --- 6" 77 --- Rear Springs 7" 71 80 8" 66 75 9" 63 --- 10" 59 --- We find that the rear suspension must not exceed 90 per minute as an absolute maximum or the rear passengers will be thrown. If the front suspension exceeds about 120 per minute we find that the rear passengers will be "joggled" to and fro in their seats at any speed above 30 m.p.h. With stiff front springs it becomes impossible to get enough shock absorber effect in front to prevent this uncomfortable riding (due to "pitching" of the car) without setting the shock absorbers so stiffly as to give very harsh riding in the front seats at the lower speeds. | ||