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 discussion on rear spring lubrication, bouncing frequency, and design comparison between pre-war and post-war models.
| Identifier | ExFiles\Box 43\2\ Scan043 | |
| Date | 10th June 1922 | |
| Oyl - G 10622 -3- June 10, 1922 Gaiters packed with grease are the worst possible thing for the rear springs, since they dry out and become so stiff that they throw you at the rear continually. When the springs get in this condition we have proved again and again that simply stripping off the gaiters and feeding the forward tip of each spring plate with oil (engine oil preferably) will rectify the riding within 100 miles. At the same time we feel that you have put one over on us in giving us the so-called post-war "thins" as the equivalent of the pre-war springs. Reference to pre-war cars shows us that these have about 50% more leaves than our present "thins", in fact, the latter are only a halfway step between the old "thicks" and the pre-war springs. The pre-war springs appear to us to give better riding when lubricated than our present ones. Our design is peculiarly adapted to lubricating in this way. Oil fed gaiters may be the final solution. My explanation of this is that, at least with our form of cantilever springing, what is needed is a spring with a lot of lubricated friction (which varies with the velocity of movement) and as little dry friction as possible, and with a bouncing period at the rear fully loaded of less than 80 complete bounces per minute. Our spring formula here and at Derby allows for 8" deflection of the rear spring from no load to full load positions. Theoretically, neglecting friction, this should give a bouncing frequency at the rear, fully loaded, equal to the frequency of swing of a simple pendulum 8" long, or 66.3 complete bounces per minute. Because of the friction in the spring the period is actually quicker. When springs are dry it may be 100 and will undoubtedly fling in the rear. When springs are properly lubricated with oil it will be 70 to 80 and the car will not fling under any reasonable circumstances and will not bump except under exceptional circumstances like a bad R.R. crossing taken too fast. If the rear bouncing period is less than 80 the car will "squat" when it passes over a bump. If more than 90 it will fling. If less than 60 (due to use of extra weak springs) bumping will become objectionable. When the car is so loaded that it has a deflection of 8" at the rear from the | ||