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).
Analysis of vehicle wobbles, focusing on the effects of balloon tyres and wheel imbalance.
| Identifier | ExFiles\Box 178\1\ img117 | |
| Date | 13th July 1926 guessed | |
| - 18 - We have proved this by fastening heavy lead bands round the front brake drums, wobbles then came on at a lower speed and were more violent than before. Similarly without front wheel brakes the Rolls-Royce car was immune from high speed wobbles. The additional weight has brought up the trouble. Balloon tyres produce two results. Firstly, if a low pressure tyre is bounced, its frequency is less than that of a high pressure tyre. The result of this is that when fitted they lower the criss-cross period of the axle which is bad for wobbles. Secondly, most large balloon tyres have less plies in their casing than a correspondingly high pressure tyre. This means that at low pressures their internal friction and consequently their damping is less. What we mean is that a normal tyre at 20 lbs/sq. in. is a poor object for bouncing, an 8" balloon tyre at the same pressure, however, has plenty of resilience. High pressure normal tyres run at low inflation pressures also lower the road speed at which wobbles occur. A large number of items come under the second heading, the most important of which is wheel balance. If a wheel is out of balance, once per revolution, a direct pull is exerted at the extremity of the axle tending to lift it into the air. The extent of this force is shewn by the fact that 1 lb. out-of-balance in the tread of the tyre will exert an upward pull of 160 lbs. once per revolution of the wheel at 60 m.p.h. Therefore if the axle has any tendency to vibrate in a criss cross manner, any out of balance p' contd. | ||