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).
Investigations into low-speed wobble, castor angle, and steering issues.
| Identifier | ExFiles\Box 95\1\ scan0351 | |
| Date | 29th September 1936 | |
| -5- Hs{Lord Ernest Hives - Chair}/FDH.14/KM.2)29.9.36. Reducing the castor angle would reduce both ill effects of the flexible steering system as there would be less wind up when cornering and the tendency to low speed wobble would be reduced. Unfortunately, the large change of castor angle between the normal and the bump position makes this unwise at present as we are already on the verge of trouble due to wandering when braking. The Wraith wheel movement should improve this situation as the change of castor angle will be about one third of the present amount. The effect of castor angle on low speed wobble tendencies is quite marked, as 30-MX{John H Maddocks - Chief Proving Officer}, which is low at the front and probably has about 1° less castor than standard, will not wobble with a 950 lbs/ins/degree steering. The standard car will just wobble, if started by the driver, at 1200 lbs/ins/degree. Brief tests were also carried out on the effect of different tyres and the addition of a front roll rod. There was no measurable difference between standard tyres and wheels and the same tyres on wide rim wheels. Bentley racing tyres made the joggle considerably worse, presumably because of their less internal damping. The roll rod had no effect on the amount of joggle, but raised the frequency of wheel hop slightly. Since completing the above tests on the bumper drums there have been several complaints of low speed wobbles from trials and customers' cars, and accordingly we have made some further tests on this trouble. Low speed wobbles on the Ph.III have been brought up partly by the elimination of set-up load on the side steering tube springs and also largely by the crowning of the tyre treads for the purpose of silence. So far we have eliminated the wobble on three cars by increasing the friction of the cross steering tube joints from the standard figure of 3/7 lbs/ins. per joint to 75-100 lbs/ins. per joint. Fortunately this increased friction is hardly noticeable at the steering wheel and is not objectionable. The increase is obtained by splitting the upper ball pad to the attached Rm.{William Robotham - Chief Engineer}179 to prevent it rotating and, in addition, by packing up the springs as much as possible. The latter is a temporary measure and we hope soon to be able to recommend a stronger spring. We propose to run the increased friction load on 33-MX{John H Maddocks - Chief Proving Officer} for 10,000 miles test as soon as the parts are ready. Hs{Lord Ernest Hives - Chair}/F.J.Hardy. | ||