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).
Analysis of vehicle pitching speeds and the factors that influence them, such as springs, weight distribution, and wheelbase.
| Identifier | ExFiles\Box 43\2\ Scan182 | |
| Date | 10th November 1926 | |
| Oy13-E-111026 -3- November 10, 1926 (4) We conclude that the larger car requires much softer springs than the smaller car, for a given pitching speed because its radius of gyration is less in proportion to its wheelbase. More particularly, if "k" is the radius of gyration, "a" the length from front axle to C.G., "b" the length from rear axle to C.G., we suppose that the ratio k²/ab is less for the larger car than it is for the 20 hp. (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 lb. trunk was added at the back. Corresponding pitching speeds, without changing the springs, ran from 124 per minute to 115 per minute. (6) By adding (theoretically) 500 lbs. on the trunk rack we get k²/ab = .665 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 center 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 things 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 minute 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. | ||