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 analysis of vehicle suspension characteristics, including pitching speeds, spring rates, and axle pad effects.
| Identifier | ExFiles\Box 43\2\ Scan178 | |
| Date | 11th October 1926 guessed | |
| contd :- -3- (5) The ratio k²/ab (for the sprung weight only) on the two cars we were testing ran from .455 to .53, the latter when a 200 lbs. trunk was added at the back. Corresponding pitching speeds, without changing the springs, ran from 124 per minute to 116 per minute. (6) By adding (theoretically) 500 lbs. on the trunk rack we get k²/ab = .685 and pitching speed down to 110 per min. This distribution we think would in practice be close to the ideal condition where oscillations at either end would not affect the other end. (7) Adding four passengers to a car reduces k² slightly in every case, but lowers the pitching speed slightly in spite of this because of the increased spring deflection. (8) Softening the front springs reduces the pitching speed a lot and the bouncing speed slightly. Softening the rear springs 400 lbs. each (2200 to 1800 lbs.) has little effect on the pitching speed, but shifts the centre of oscillation backwards i.e. reduces the vertical movement at the rear for a given front movement. (9) Increasing the wheelbase from 143-1/2" to 146-1/2" will increase the pitching speed from 116.5 to 117.5 oscillations/min., other thing remaining the same. (10) From our observations of cars at the works we believe that for some reason unknown to us, pitching at a frequency higher than about 120 per min. is very objectionable, particularly to the rear passengers who are lifted up and down (whereas the front passengers sit practically on the centre of oscillation and only rock to and fro). In this connection many rear seat backs and cushions have been found objectionable because of being undamped. (11) Effect of wide axle pad. We inspected the springs off the l.h. drive Phantom referred to with a heavy clip representing the wide axle pad on the new type front axle. We found that clipping the springs increased the stiffness 14%. (This agrees with the calculated stiffening effect when the plates between the U bolts are considered inactive.) On other springs this stiffening effect is as low as 8%. It appears to vary with the flatness of the short leaf. Also it is necessary to get negative camber on the spring when tightening it to get the max. stiffening effect. contd :- | ||