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).
Rear spring friction, with comparisons to Cadillac vehicles and a table of theoretical formulae.
| Identifier | ExFiles\Box 173\2\ img030 | |
| Date | 9th February 1934 | |
| February 9, 1934 Mr. E.{Mr Elliott - Chief Engineer} W. Seaholm Chief Engineer M.{Mr Moon / Mr Moore} Olley Cadillac Motor Car Company SPRING FRICTION Working on the question of rear spring friction in the light of what we know from D series Cadillacs, Mr. Crane's A series 16, the dynamic rear spring tests, and experience with the Rolls Royce cantilevers, I have tried to get an indiction of how much friction is desirable. It seems obvious that we do not have enough friction in Series 10 and 20 to get the best boulevard ride, and Cadillac experience right along has been that boulevard ride improves up to a certain point with drying out of the springs. Rolls Royce experience was exactly the reverse. Mr. Robotham has repeatedly brought up the ride of the cantilever-sprung Rolls which I took to England in 1930 and which had a degree of "quietness" in rear end action not equalled by Rolls-Royce before or since. This was obtained by very careful spring bedding construction of springs without nip and lubrication with engine oil at intervals of not more than 1000 miles. The weights of this car, both sprung and unsprung were very similar to a Series 30 Cadillac. Tires were 19x7 at 35-40 lbs. The first thing to find out is whether there is any essential difference in friction between a pivotted cantilever and a flat spring. This depends on the way in which the springs are designed. The following formulae appear to be as correct as one can expect from a theoretical treatment:- FRICTION FORCE AT WHEEL | | SIMPLE CANTILEVER | FLAT SPRING | PIVOTTED CANTILEVER | | :--- | :--- | :--- | :--- | | Simplest relationship | μWt(N-1) / l | μWt(N-1) / l | μWSl(N-1) / h² | | Based on volume of spring (active metal) | (f t²(N-1) / 3l³) * μ * Vol | (f t²(N-1) / 3l³) * μ * Vol | (f t²(N-1) / 6l³) * μ * Vol | | Based on rate and stress | (μfSt/E) * (N-1) | (μfSt/E) * (N-1) | (2μfSt/E) * (N-1) | | ||