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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 causes, characteristics, and remedies for different types of steering wobble and shimmy.

Identifier  ExFiles\Box 170\3\  img061
Date  15th July 1935 guessed
  
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It also follows that softening the steering mechanism, by springs in the drag-link, or by a shimmy damper, slows down the natural frequency of wobble and therefore tends to cure shimmy at the expense of creating a tendency to low speed wobble. The shimmy damper is the more effective because this not only softens the steering mechanism but also adds to the mass of the vibrating system and therefore slows down the wobble oscillation more than the soft drag link.

This explains the effectiveness of a very old cure for shimmy on axle cars, in which it was usual to soften the drag link with springs until shimmy was gone and low speed wobble appeared.

The low speed wobble was then damped out by adding friction in the kingpin or tie-rod joints.

Since the energy input in low speed wobble is very small (compared with shimmy) it was found quite possible to damp out the wobble without making the steering heavy.

The wander generally appear to be improved by some additional flexibility in the steering.

The tramp on the other hand are made worse by increased flexibility and are improved by stiffening the steering gear in its mounting or cast.

Several different varieties of low speed wobble have been distinguished, each of them associated with a distinct and different rocking motion of the car. The one described above is the common type, but in the case of a broken steering gear, disconnected drag link, or excessive slack in the steering, a more violent wobble occurs at 15 cycles a minute, associated with a rocking of the car about a horizontal axis approximately through the bottom of the windshield.

In case of a broken steering this wobble can be so violent as to threaten to turn the car over.

Both cycles are sensitive to road speed, low speed wobble so far produced has a worst speed of 30 m.p.h.
  
  


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