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).
Page discussing the principles of dynamic and static balance, and their effect on wheel shimmy and steering.
| Identifier | ExFiles\Box 29\1\ Scan117 | |
| Date | 8th October 1925 guessed | |
| contd :- -20- m w^2 d1 = P/g w^2 d2 One does not bother about dynamic balance which in this case is not present if the centre of gravity of the masses m and p are located in the same perpendicular plane to the axis of the hub. (We sum up by saying that body turning with uniform angular velocity about its axis is statically balanced when its centre of inertia coincides with its axis and is dynamically balanced when its axis of inertia coincides with its axis of rotation). It should be observed, however, that the steering as we consider it should be, ought not to be affected by a static or dynamic out of balance of the wheels less than .66 to 1.1 lbs. otherwise the motorcar will become a scientific instrument. We have proved that static out of balance promotes shimmy with 820/120 cables if it exceeds 1.75 - 2.2 lbs. measured at the periphery of the outer cover, and the car speed exceeds 55 to 60 m.p.h. The resultant reactions are not the same on different types of cars (whose stationary steering is lighter or heavier). With 33.6" Comfort tyres inflated to 21.4 lbs/sq.in. it starts bouncing which becomes a shimmy if the out of balance exceeds 500 to 600 grms; and the speed attains 45 to 50 m.p.h. on cars of the 12 HP. Renault type. When the out of balance exceeds 3.3 to 4.4 lbs shimmy is very violent and has a period exactly equal to a wheel rev. which is easily explained. contd :- | ||