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 factors causing wheel shimmy and recommendations for improvement.
| Identifier | ExFiles\Box 170\2\ img244 | |
| Date | 12th January 1935 guessed | |
| -6- that results in shimmy. We have this pretty well proved, although I cannot go into details at the present time. Nine factors seem to affect wheel fight (or shimmy):- (1) Degree of parallel action. (2) Torsional frame stiffness. (3) Engine mount. (4) Mount of steering gear. (5) Shock absorbers. (6) Reversibility of steering. (7) Damping in steering mechanism. (8) Tires. (9) Wheel inertias. If (2) or (3) are poor, (1) must be good, and so on down the whole range. Apparently you have to face a condition where (2) is necessarily poor, and where (6) is necessarily high. With (2) poor you cannot do much with (5). So one would guess that (1) must necessarily be made high to escape trouble. In this case I should say you must positively fit a front stabilizer for best results. Rear end kick (on long waves). Inertia shock absorbers at the rear act as snub-straps to hold this. (So long as the amount of orifice is not excessive.) But it is really an effect of "front to rear" resonance on a soft-sprung car. Stiffening up the rear rebound setting helps. Moving rear seats forward or rear axle back helps enormously. Making the front deflection about 10% greater than the rear deflection at normal load, helps. Stiffening up the bump setting on front shock absorbers helps. Fitting rebound snub straps on the rear axle helps. (Incidentally I don't think your standard method of taking deflections is worth a damn. Only way seems to me to mount the car on four platform scales and push it up and down with jacks and measure deflections and loads direct. Then deduct tire effects. The "deflection" is normal load divided by stiffness at normal load). Sludge effects. Mobiloil D is too heavy. | ||