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).
The principles of tuning a steering mechanism to avoid wheel fight, wobble, and shimmy.
| Identifier | ExFiles\Box 170\3\ img025 | |
| Date | 26th March 1936 guessed | |
| -2- (3) Tuning Steering Mechanism. The most potent factor in determining wheel fight is the "tuning" of the steering mechanism which fixes the natural frequency at which the wheels oscillate round the kingpins ("flap frequency"). Almost all cars with successful steerings are tuned to a flap frequency between 450 - 500 cycles/min., which is a range almost equally spaced between wobble and shimmy, but favours the low frequency or wobble side. If the steering is tuned to the wobble frequency, say 380 a minute, the wheel fight will be a violent wobble. If the steering is tuned to a frequency of 600-700 a minute, the wheel fight will occur when the wheels hop and will resemble a shimmy. Unbalanced wheels will probably cause an actual shimmy on smooth roads at 60 m.p.h. with this tuning. The Chevrolet master is tuned between 420 and 440 and shows a distinct wobble tendency. A notable exception is the Chrysler 6 which is tuned high, 560, and escapes shimmy only by a special high frequency of engine mount. (4) It is desirable to favour the low frequency side in tuning the steering because :- (a) The sequence of bumps which cause wobble are more rarely encountered. The factor of probability favours low frequency. (b) Wobble, being slower, is more easily damped out by friction in the steering. (c) Wobble is more effectively damped out by "harmonic balancer" action of the engine. (d) The more flexible steering mechanism cushions the shocks on the steering gear and wheel. | ||