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).
General conclusions on the causes and contributing factors of steering shimmy, with analysis of tyre types and specific car models.
| Identifier | ExFiles\Box 29\1\ Scan119 | |
| Date | 8th October 1925 guessed | |
| contd :- -22- We do not believe that this distortion plays an important part in the production of shimmy. GENERAL CONCLUSIONS. (1) Shimmy affects the steering of numerous late model cars fitted with low pressure tyres when the critical speed is reached. We know that older model cars without front wheel brakes are practically immune from wobbles. In order that shimmy may occur it is not essential that play should have started in the steering. Several cars whose steering has little, or practically no play, shimmy! (2) With small section tyres 3.7" and below, shimmy is rare. The 10 HP. Renault whose steering is heavy has practically no shimmy! On the other hand the Lambda Lancia whose steering is light, is very prone to shimmy. With 6 ply tyres (4½") there is little tendency to wobble. The 360/160 seem to be the wobble promoting tyres. These results are self-explanatory. We have seen that the thinner the wall of the tyre, the greater is the lateral displacement possible and the more numerous the chances of wobbles, starting. Low pressure tyres have considerable faculty for storing up energy and restoring it when there are shocks between the road and the wheel. With cables, on the contrary, whose walls are stiff and difficult to distort, there is no shimmy. We have even observed a case where a single cable on the front sufficed to suppress wobbles. contd :- | ||