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).
Comparison of chassis and suspension characteristics between the 40/50 HP and 20 HP models, focusing on the causes of roughness.
| Identifier | ExFiles\Box 67a\1\ scan0050 | |
| Date | 31th December 1925 | |
| - 3 - BYLL/H.{Arthur M. Hanbury - Head Complaints} 31.12.25. From the foregoing it should now be amply clear that the problem is a very involved issue, and not one to be treated like the knot of Greek mythology. I am not trying to controvert observed phenomena, but merely trying to prevent a remedy being hastily adopted which may prove worse than the disease. There are many different factors besides vertical resilience which affect riding comfort, and it is obvious that it is these factors which are at the bottom of the differences that undoubtedly exist between 40/50 HP. and 20 HP. chassis. In my opinion, the roughness complained of is more likely to be the result of side shocks to body and not vertical effects at all, for the following reasons:- a/- The cantilever spring is, in my opinion, relatively stiffer against side movement than the semi-elliptic as it has one half of its length securely braced to the side channel and projects the stiffness of the braced end to the free end at the axle. b/- The cantilever spring again demands very much more steel than the semi-elliptic and the massed section is not so easily distorted torsionally as is the semi-elliptic which again creates lateral stiffness. c/- The cantilever spring has wider plates and is actually stiffer as a result of dimensional differences in ratio of 100 to 65. d/- The 40/50 is suspended higher, i.e. the end of spring is 3.5" above centre line of axle, while in 20 HP. it is 2" below. By this the 20 HP. is considerably relieved of side loads from centre of gravity of chassis, being relatively very much lower than in the case with the 40/50. e/- The 40/50 HP. axle is arranged for a very much greater vertical movement of axle than the 20 HP. and this demands greater lateral flexibility in the 40/50 HP. than the 20 HP. whereas the former is by all design issues stiffer laterally than the latter. BY.{R.W. Bailey - Chief Engineer} [Signature] | ||