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).
Reviewing the position of road springs and the effects of fitting low-rating springs on riding quality, steering, and braking.
| Identifier | Morton\M19\ img067 | |
| Date | 13th May 1931 | |
| To F.{Mr Friese} From Hs{Lord Ernest Hives - Chair}/An. c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to Da.{Bernard Day - Chassis Design} R.{Sir Henry Royce} c. to Wy. P. Hs{Lord Ernest Hives - Chair}/RM.{William Robotham - Chief Engineer}3/RT.13.5.31. X7410. X5410. ROAD SPRINGS. We think it may be advisable to review the present position of road springs. We are now in the process of improving the riding qualities of our cars by fitting low rating springs. There is no doubt that this alteration greatly reduces the "pitching" tendency and softens the suspension below 50 M.P.H. Our tests have shown that the front springs have more effect than the rear springs. We tried front springs on the 40/50 and on the 25 HP. of intermediate softness (4.1" & 3.375" initial deflection) but were disappointed with the results. Springs 16.G.IV. and 18-EX. have the recommended front springs (4.5" & 4.0" initial deflection) that are being standardised. In view of the fact that, when we use these low deflection springs, we are asking the suspension to do work for which it was not originally designed, we point out the following disadvantages which accompany the improvement in riding comfort. (1) Steering shocks and lack of selectivity. As soon as we reduce the rating of the front springs we increase steering shocks and joggles, we also spoil the directional stability of the steering. This is far more noticeable on the 40/50 than on the 25 HP., the latter car has not yet reached the state when we should expect it to be severely criticised. We attribute some of the lack of selectivity to the very thin top leaves that have to be employed to keep the stress down, these leaves have to control the axles laterally and also on the front of the 25 HP., the fore and aft pivot lean. (2) Effect of Braking. The 25 HP. relies entirely on the spring to take the braking torque. The 40/50 puts the top spring leaf in compression when the brakes are applied. The thin top leaves do not behave very satisfactorily when put in compression; judging by watching the spring when the brakes are applied the stresses must be high. | ||