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 letter detailing the causes and cures for wheel wabble and wheel fight.
| Identifier | ExFiles\Box 170\2\ img289 | |
| Date | 27th August 1935 guessed | |
| -5- (6) Continued: (a) Continued: (4) Continued: When wabble occurs they run at the same frequency, but a phase difference exists between them such that the road feeds energy into the wabble and the wabble feeds energy into the rocking of the car. (b) Wheel fight is not pure wabble, but if wheel fight exists pure wabble conditions are not far off, ie, a slight decrease of friction or increase either of backlash or flexibility in the steering system will produce wabble. (c) Wabble and wheel fight depend almost directly on caster. That is caster angle or caster offset on the ground is the principal excitation. Reducing caster is obvious method of reducing wheel fight. (d) Other cures of wheel fight or of low speed wabble are along following lines: Effective cures are:- (1) Stiffening the steering mechanism, steering gear, or steering gear mount. (In this it appears the reverse of shimmy in which a softer steering mechanism is generally an improvement). (2) Reducing reversibility of the steering gear, which of course is just a particular case of (1). (3) "Tuning" the rubber engine-mounts, so that the rocking frequency of the engine is the same as the wabble frequency. In this case the engine acts as a harmonic balancer and prevents the wabble from building up. The tuning must be very close. (4) Miscellaneous items such as:- (a) Increased shock absorber action. (b) Avoiding backlash anywhere in steering or kingpins. (c) Torsional stiffness of body frame assembly should exceed 3000 lbs feet per degree between wheel centers. Etc. If you should make similar tests and get anything interesting you might let me know. Sincerely yours, Maurice Olley | ||