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).
Technical analysis and comparison of Packard-type independent front suspension.
| Identifier | ExFiles\Box 127\1\ scan0282 | |
| Date | 1st February 1937 | |
| E.{Mr Elliott - Chief Engineer} from Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} c. to Sg.{Arthur F. Sidgreaves - MD} c. to Hs.{Lord Ernest Hives - Chair} c. to Da.{Bernard Day - Chassis Design} c. to R.{Sir Henry Royce} PACKARD TYPE SUSPENSION. Owing to the fact that our Packard car has a tendency to dip its bonnet when its very powerful hydraulic-bendix brakes are used, it is thought that the particular type of independent suspension fitted to this car tends to make the car dip in front when a brake couple is applied. This is an entire misapprehension, probably due to the fact that no layout drawings are available. The sketch herewith shows that the Packard independent suspension is an ingenious system of fitting a pair of unequal link forward facing triangle levers to a chassis. A wide front tray is not required, and the designers have, therefore, had metal to spare to make it deep and thus resist cross torque. On our P.III when the front of the car dips, the castor angle is reduced, and the same is true of Wraith; that is to say that the brake torque actually assists the front of the car to dip, by the theory of work. The Packard system is equivalent to running a P.III backwards, therefore the castor angle is increased when the front dips, and the brake torque resists this movement. An extreme form of our suspension is the Dubonnet with the wheel behind the steering pivot in which a torque arm is necessary to keep the castor constant, an extreme form of the Packard is the Vauxhall Dubonnet system in which the brake torque lifts the front of the car. Our reasons for fitting backward sloping levers were probably twofold:- (1) We did not think of a way of fitting forward sloping levers without increasing the wheelbase. (2) The decrease of castor angle on the heavily loaded outer wheel due to roll on cornering was thought to be an advantage in keeping the steering light. Olley has recently said that this action is so slight as to be negligible, and anyone who has driven the Packard must agree with this, the steering being remarkably light. | ||