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).
Front and rear spring clearances, bumping issues, and the effects of spring lubrication.
| Identifier | ExFiles\Box 43\2\ Scan042 | |
| Date | 10th June 1922 | |
| Oyl - G 10622 -2- June 10, 1922 body weight (including wings, lamps, etc.) is on the front axle. This difference sometimes means a step up of 100 lbs. on each of the front springs, which is enough to make a lot of difference in the tendency of the front axle to bump. In 1918 we asked that the upward clearance of the front spring be increased by setting the rubber block on the side of the frame instead of the bottom of the frame, so that the spring could rise to within say 3/4" of the frame before it bumped. We were told this would lead to front spring breakage because of the excessive deflection permitted. This does not strike us as a good argument because this excessive deflection is very occasional, and I think the bump is probably more destructive in its effects than the deflection without the bump. Here are some front spring clearances taken by Mr. Caswell a year ago, for comparison: Crane Simplex - Front 4 3/4 to 5 Rear 8 1/2 to 9 1/2 Brewster " 4 1/4 to 4 3/4 " 7 1/2 to 8 1/2 Rolls-Royce " 3.3 " 7 1/2 normal load 5 1/4 full load It will be seen that we are very shy on front clearance. The tendency of the cars to bump in front confirms this. While on the subject it is well to take up the question of rear springing on which we have had some interesting experiences which go to contradict the idea that the thick and thin leaf springs are similar when lubricated. The tests which led you to make this statement some time back were, I believe, static loading tests. We are convinced that the statement does not apply to springs in rapid movement on the car, in which case it is necessary to keep our present rear springs thoroughly lubricated with oil in order to get good riding of the car. In fact, we find that when the springs are rightly proportioned to the weight of the car, the only thing necessary to get perfect riding qualities is periodical oil lubrication of the rear springs. Shock absorbers not only are unnecessary but are a disadvantage. | ||