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).
Weight balance around the kingpin and the effects of caster on steering.
| Identifier | ExFiles\Box 170\3\ img048 | |
| Date | 14th July 1933 guessed | |
| -16- "tuning" of the engine to frame frequency which must exist in these two cases is not yet understood. Frame stiffness, can also have an influence. Increasing the stiffness of the nose of the frame by triangular tube stiffness, on the TT job, gives a noticeable improvement. Weight balance around kingpin. The fore and aft position of the centre of gravity of the swinging mass relative to the kingpin centre line, must have an effect on the wobble cycle, but from our observations and figures this effect is not large and it is by no means clear from calculations whether the centre of gravity ahead of the kingpin may be an advantage when all factors of the steering of the car are taken into consideration. The effect of position of centre of gravity is chiefly indirect. The car with the centre of gravity ahead of the kingpin derives a lot of "road feel" from centrifugal force at the centre of gravity of the swinging mass. It therefore may run with less caster or actually with negative caster without losing its sense of direction entirely. When the centre of gravity is behind the kingpin centrifugal force on the swinging mass acts in opposition to the caster. For a given road feel the caster must therefore be increased, and since increasing caster increases wobble excitation, the necessity of either tuning out or damping out wobble is more apparent on a "pusher" type Dubonnet than on the "puller" type. This difference is considerable, for example as between the Chevrolet Master and TT job our measurement show that for a "completely zero" caster condition (i.e. a condition in which precession torque only is relied on to guide the wheels) the Master will have 2º negative caster (or ¼ inch negative offset) and the TT 1-1/2º positive caster (3/8 inch positive offset). It may be objected that there are a lot of conditions under which caster is effective but where centrifugal force is small. (such as shunting a car at low speeds). This is undoubtedly true and as a result we suggest that the best all round position for the kingpin line inside elevation is through the centre of gravity of the complete swinging ass, thus :- | ||