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 wheel shimmy, exploring the effects of wheel weight, front brakes, and steering play.
| Identifier | ExFiles\Box 29\1\ Scan107 | |
| Date | 8th October 1925 guessed | |
| CONTD :- -10- This wheel tends to slow up, while the other tends to accelerate and one can imagine an explanation of shimmy based on these considerations. Weight. (a) If one considerably increases the weight of each of the wheels to the extent of 200 to 300%, the intensity of the shimmy is diminished and the critical speed is lowered. Loading each wheel with peripheral masses weighing 28 lbs., the critical speed falls to 37 - 40 m.p.h., and the intensity of the wobble diminishes. We think in this case the gyroscopic effect becomes preponderant and opposes the starting of the shimmy. (b) We have observed that with lighter wheels than the Michelin, shimmy appears to be just as violent. (c) If one diminishes the unsprung weight (front axle) the intensity of the wobble is also reduced. This has made people say that the wobble is due to the presence of front wheel brakes which increase the unsprung weight. This however is not altogether correct. Front wheel brakes have in reality made their appearance at the same time as steerings which are light and low geared. These latter, of necessity, require considerable inclination of the pivots which fact is favourable to shimmy. There are cars that exist without front wheel brakes which will shimmy and conversely. Front wheels brakes therefore only increase the violence of the wobble due to their weight. D.{John DeLooze - Company Secretary} STEERING. (Portion of test omitted). Play in the steering. (Michelins have a method of measuring the play in the steering which enables them to compare different types of cars. They give a definite limit which is likely to produce wobble but it is not of much use to us.) OMITTED CONTD :- | ||