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 report on major problems with the Ph.III chassis, specifically tyre noise and gearbox chunking.
| Identifier | ExFiles\Box 173\4\ img199 | |
| Date | 1st January 1936 | |
| -4- As regards the major problems on the Ph.III chassis - (1) Tyre Noise. Most of the manufacturers agreed that the more rubber between the axle and frame, the less the tyre noise, the best results being obtained when there is a rubber pad between the axle and springs, and the spring eyes are also rubber bushed. The problem of unselective steering has then to be tackled by preventing the car oversteering. It is interesting in this connection that G.M. would use a 5 or 5½" rim for a 7.50 tyre to prevent steering wandering. The tyre manufacturers say that one has to choose between noisy tyres with good adhesion and quiet tyres with poor adhesion. The Goodyear people say the best compromise is obtained when the centre of the tyre has plain continuous ribs and the edges consist of varying sized diamonds. Rubber between the axle and frame not only helps tyre groans, but also improves the riding silence over setts and rough roads, and reduces the difficulty of obtaining quiet rear axles. A further improvement is effected by mounting the body on rubberised canvas. (2) Gearbox Chunking. The secret of a car with a slack gearbox that does not "chunk" is that this state of affairs is possible provided the clutch splines have no slack and the axle a very small amount, considerably less than our usual practice. In the common American half floating axle, it is not difficult to reduce this slack to a total of 1º at the pinion. Packard say this is more difficult to obtain with a hypoid than spiral bevel. The alternative of having no slack in the gearbox, which usually cures this trouble, is far more difficult. Both Buicks and Packards go to extreme trouble to reduce gearbox slacks, and in this connection say that involute splines can cheaply be made an excellent fit. The square splines we use are very likely to bed only on the bottom of one and the side of another, and thus little oil cushioning is obtained at the reversal of torque. | ||