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 'shimmy' or 'wobble', discussing the influence of road conditions and tyre types.
| Identifier | ExFiles\Box 29\1\ Scan105 | |
| Date | 8th October 1925 guessed | |
| contd :- -3- A.{Mr Adams} THE ROAD. Shimmy is much more violent, its oscillations are more regular, and it is sustained over longer periods when the ground is dry and smooth. On wet ground the intensity of the wobble decreases and sometimes it completely disappears. On uneven ground wobble starts but does not continue owing to lack of synchronism. At a given speed wobble is equally affected by climbing or descending. The presence of ruts in the road do not materially alter this phenomenon unless they are of a small type less than 30 yds. apart. In this case the inequality of the impressed forces (tangential, lateral, and vertical) on the front axle destroys synchronism. Conclusions. (a) The importance of the adherence, or power of gripping of the road by the tyre which determines the tangential re-action at the tyre. (b) As soon as the phenomenon is started, forces in play in the car from the normal re-action of the ground are sufficient to sustain it. Abnormal re-actions such as those due to holes and bumps tend to destroy it. These facts are characteristic of harmonic motions. B. THE TYRE. In the absence of specific information our results will be taken as being carried out on 'comfort' tyres 33.4" X 3.0" at 22.4 lbs/sq.in., for it is understood that cars with two cable tyres in front or even a single cable tyre, does not shimmy. contd :- | ||