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).
Technical analysis of steering wobble and shimmy, considering factors like play and castor angle on various cars.
| Identifier | ExFiles\Box 29\1\ Scan108 | |
| Date | 8th October 1925 guessed | |
| contd :- -11- Inner lash In The new 12-HP. Renault without appreciable play, the steering has hardly any tendency to wobble. When play increases however, shimmy appears. If the phenomenon persists, wear very rapidly increases and the wobbles increase. Conversely they disappear if one takes up the play. The worst wear is that on the parts of the steering box. It is this which is the most difficult to remove and is the most usual cause of wobbles. We have tried cars (Chenard, Lancia and Fiat) which in their new state and without any slack in the steering connections, wobble. Conversely, old model cars of 1918 have plenty of play in their steering but with no shimmy because their heavy steerings prevent the start of wobbles. Conclusion. Play in the steering is not a sine qua non of shimmy but it favours a wobble starting and increases its amplitude. Castoring and anti-castoring. Castoring increases the lateral stability of the car when it tends to leave a straight path. Usually, the angle of castoring is 2° or 3°. When this limit is exceeded the violence of shimmy increases. With 11° castor however, the car can still be driven without danger. Anti-castoring reduces shimmy. We have tried successfully 3, 6 and 11°. At 11° shimmy was much reduced but not eliminated. Conclusions. It is well not to exceed 1° to 2° of castoring contd :- | ||