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).
Shock absorber valve settings and their effect on vehicle ride quality.
| Identifier | ExFiles\Box 55\4\ Scan347 | |
| Date | 11th April 1929 guessed | |
| - 2 - The alternatives are seldom used even in service. I think the rear poundage could just as well be made 120 lb. up and down, but we have not proved this yet. The L.P. valve is set by blow off pressure. The H.P. valve is set by lbs. load on the valve spring. The information on ball lbs, oil pressure, and valve poundage from which we are working is given in my note to you OY3 of last July 13th. Prints of the valves and relative leakage figures are attached. Your tests seem to show conclusively that for movements of large amplitude the small leakage of the valve has negligible effect. Also that the oil velocity for an allowable axle movement is about twice as great as the oil velocity for an allowable car movement, so that if a leaking valve will adequately "hold" the car it will certainly permit adequate damping of the axle. In other words 70 cycles/min. and 4" stroke (bouncing) or say 140 cycles/min. and 2" stroke (pitching) will only produce half the oil velocity of say 560 cycles/min. and 1" stroke (axle movement.) It therefore is not easy to see how the leaking valves (particularly if the poundage on the valves was raised when the leaking valves were fitted, as can be done without jerky riding) can do anything but increase the road holding ability and riding quality of the car at speed in proportion to the increased poundage, since under high speed conditions the leak is negligible. I would suggest further that the riding quality in the rear seat of the S.S. at high speed is probably controlled as in the Phantom scarcely by the rear shock absorbers at all, but almost completely by the front shock absorbers. It has always been our finding that the chief functions of the rear shock absorbers are first to hold the axle on the road, second to prevent rolling and perhaps third to prevent sea sickness through excessive rear spring movement (i.e. bouncing). The 120 cycle pitch is what we have always found to cause uncomfortable riding and is controlled almost entirely by the front shock absorbers and that is why we have raised the poundage and reduced the valve leakage in the front shock absorbers to the limit consistent with good low speed riding. I would suggest therefore that if the front shock absorbers on the S.S. were set 120 lb. up and down and fitted with slightly leaking valves like A-12293 to take off the "harshness" at low speed, the car should ride well at high speeds. -continued- | ||