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).
Continuation letter from Dunlop Rubber Co. Ltd. discussing the causes and effects of wheel wobble in relation to tyres and road conditions.
| Identifier | ExFiles\Box 28\4\ Scan334 | |
| Date | 1st August 1925 guessed | |
| A121 D.{John DeLooze - Company Secretary} R.{Sir Henry Royce} Co. LTD. CONTINUATION SHEET No. p. 2. 19 Further, your previous results with high pressure tyres, showed that the wobble may be maintained, even when the two periods referred to do not coincide. The most important point arising out of the test on balanced balloon tyres is that a wobble of considerable amplitude can be built up in a very short time. This could hardly be accounted for by the minute amount of wheel bias, and we must conclude that the whole axle system tends to fall into a certain type of vibration, and does so on the slightest provocation. This may be illustrated by the case of a simple pendulum. If the point of support be moved in any irregular manner, and then brought to rest, the pendulum will continue to swing in its own period. We agree with the point made in your second paragraph, viz., that there is no reason why the axle should not take up criss-cross vibration at any speed, providing that the wheels receive impulses from the road at suitable intervals of time. However, at low speeds the gyroscopic effect is small, and there is no tendency for the axle system to build up a vibration on its own account. As soon, therefore, as the particular road waves are passed, the vibrations will disappear, and during the whole process there will have been no "steering wobble". We do not consider it necessary to have a long sequence of regular road waves in order that a wobble may be built up, and your hypothetical case seems to us of little value. It is impossible to deal with the case of ruts in a mathematical manner, but it is obvious that if ruts at intervals of 10 yds. excite a wobble at a certain speed, then ruts at intervals of 20 yards would excite a wobble at the same speed. If the road irregularities are undulatory, as is more probable, then the mathematical analysis given in the paper holds good, and twice the speed would be required for the longer intervals. We would say that transverse ruts would have no effect even if they occurred, because they would cause very little disturbance to a car passing over them at high speed. Yours faithfully, A Healey. for Dunlop Rubber Co. Ltd. | ||