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).
Wheel oscillations and balance, specifically investigating the causes of shimmy related to tyre patches.
| Identifier | ExFiles\Box 29\1\ Scan118 | |
| Date | 8th October 1925 guessed | |
| contd :- -21- The diagram that we have taken (see test 18.) shows the regularity of the oscillations. Out of balance of the wheels actually plays an important part in the production of shimmy and it is essential, in producing high speed cars, to balance the whole wheel, inner tube and tyre. We should like to point out the danger of fitting patches. We have measured 2.42 out of balance after 900 klms. running with a patch, this provoked violent shimmy. The out of balance was due to :- (a) The weight of the patch. (b) To wear on the tyre immediately opposite to the patch. This wear is accounted for by the effect of centrifugal force which tends to lift the wheel and to make it spin on the ground when the patch is diametrically opposite to the point of contact. We are continuing tests on the subject of the dynamic out of balance of the front wheels. As we have not got a machine permitting the measurement of this out of balance, we proceed provisionally as follows. The front axle of the car was lifted up. One of the wheels was driven by a mix variable speed motor by a rubber belt. We proved that at 600 revs. per minute(55 m.p.h.) the wheel statically balanced was out of balance dynamically and had a movement something like a shimmy but of very small amplitude which started and was maintained. We have also measured the deformation of the tyre due to centrifugal force. This attains .1 to .15" measured radially in the plane of the wheel. contd :- | ||