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).
Chassis vibration, steering geometry, and oversteering, with references to a Vauxhall 14.
| Identifier | ExFiles\Box 153\1\ scan0060 | |
| Date | 23th September 1937 | |
| -2- Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer}1/AP.23.9.37 advantage of the Holkenberger layout is that the steering gear is not connected to this crossmember. The geometry with the Holkenberger layout can be made good for bouncing but not for rolling. A Vauxhall 14 was seen running on their bumper drums and low speed wobble at 400-410/min and wheel hop at 600/min were noticed. Olley also pointed out a form of vibration at twice wheel hop frequency which can occur with both Dubonnet and wishbone systems. This vibration consists of the road wheels flapping about the king pins in opposition to one another so that the wheels are alternately toed in and out. This vibration is not felt on the steering wheel as the centre steering lever is the node, but is noticeable as a general chassis vibration, particularly on the floor in the front of the car. It can also cause high loads in the cross steering tubes and levers. The cure is to avoid resonance. It occurs to us that this form of vibration may be the cause of the irregular tyre wear which occurred on Wraith in France and we suggest that this should be investigated. In connection with the Holkenberger layout we asked how they satisfied the Ackermann principal. Olley's reply was that they did not, and in any case the centre of a turn is more nearly in line with the front wheels than with the back, and in some cases may be ahead of the car. It would therefore appear that there is not much point in the Ackermann principal. Vauxhalls have attempted to cure oversteering resulting from excessive rear roll rating by reducing front tyre pressures, but ran into excessive front tyre wear. Olley prefers to have the same tyre pressure all round and to obtain understeer by adjusting the proportion of roll rating front to rear. The best proportion is 55% on the front. Vauxhalls have at least as much trouble as we do with the Adamant Engineering Co. Chassis Vibration Investigation Olley is a great believer in the use of bumper drums with small ramps spaced at about 3 ft. intervals for general chassis vibration investigation. The Vauxhall drums are approximately 24ft. in dia. and mounted so that the tops of the drums and about 4ft. above floor level. It is therefore possible to watch the car from underneath. The underside of the chassis is brilliantly illuminated and it is remarkable how clearly the deflection of the 14 HP. frame, and the position from which it occurs, can be seen. Olley says that the value of these drums continued | ||