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 of wheel wobble, shimmy, and potential methods for elimination.
| Identifier | ExFiles\Box 29\1\ Scan120 | |
| Date | 8th October 1925 guessed | |
| contd :- -23- (3) We have not found a satisfactory explanation of the forces promoting wobbles. The fact that the wobble period is almost always exactly equal to that of a wheel revolution, has made us think that out of balance of a wheel plays an important part. We have no explanation of our results with perfectly balanced wheels. Our tests on these lines are proceeding. We have not been able to establish the part played by the distance between the hub and ground when running. When the wheel meets obstacles, this distance varies considerably (15 to 20%) when the tyre is alternately compressed and extended. Again, the tyre distorts under the action of centrifugal forces (.100 to .150" for 33.6" tyres measured radially). The result of this is that as the wheels have to traverse equal distances in the same time they have to rotate at different angular velocities, which may be a possible cause of shimmy starting. (4) We have found no means of definitely eliminating wobbles on all cars, without reducing the lightness of the steering or introducing into this delicate piece of mechanism, palliatives prejudicial to safety (hydraulic dampers etc.) (5) In the actual steering which has not changed in principle since the invention of the car, the cross steering tube is the first item which one should strive to modify or eliminate; it is owing to this item that wobbles can transfer themselves from one wheel to the other, sustain and amplify themselves. Lancia's have taken an original step in eliminating the front axle which contributes to the synchronisation of wobble. They have not banished wobbles because nothing has been altered contd :- | ||