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).
Chassis torsional stiffness, engine mounting, vibration damping, and proposed design improvements.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan101 | |
| Date | 8th April 1931 guessed | |
| (2) Now we come to a still further idea of using 2 front arms and 2 arms from the gearbox to the cross member behind the gearbox, for the object of getting the most efficient torsional stiffness from a soft mounting. Such a scheme should be tested: it may be a hardly good enough vibration insulator for a big 6 but might be good for the 25HP. I want to impress upon all concerned that we have always suffered (with others) from want of torsional stiffness of the chassis (formerly we thought it was want of lateral stiffness) but I am convinced that the latter does not worry us at the present. Bonnet wear and knocks, radiator, wings, and lamp unsteadiness all come from this trouble, and front axle excess movement etc, and since we now have the knowledge we must in our next designs profit by it. I also want everyone to realise that after we have done all we can even with the assistance of the engine we shall still be too flexible torsionally so we must in our improved designs be able to take full advantage of the engine. It must be interesting to find how bad the Hispano is which we believe is still firmly bolted into one with the frame. It will be understood that Bentley cannot have solved this unsolvable problem but must like ourselves have made some more or less imperfect compromise. Balloon tyres and more vigorous shock dampers are asking for greater stiffness in the frame which naturally will enable us to get better steering and road riding qualities because of the more effective front damping. Increase in road speeds have demanded these more effective dampers. You will remember that I took up the position that our 6 cyl. P.1. & P. 2. engine could be made better so that we could reduce the trouble at the source and after suggesting working at every possibility we have only been able to make the engine a little better at very high speeds, and that our imperfection of flywheel mounting, any crankchamber deflection, or any other curable faults have been found to have no influence on body booms, and we can only modify the effect on the body by altering the mounting and accepting a less rigid chassis, which my experience here says is worse than the trouble reported. I think we must find a better compromise, such as softer rubber in the rear feet or the suggestion in this letter of feet off the gearbox, as I recommend for J.{Mr Johnson W.M.} S. since I cannot see how we can alter this engine from 6 cyl. while we have 6 on the big car. Had we got our own steel bodies as in USA. we might compromise by trusting to those of known qualities to stiffen our chassis. The static tests I have lately suggested for complete chassis should have the prompt and constant attention of one of the juniors; I suggest Mr. Leslie and Mr. Grylls could do this and give us the degrees say per 1000 in. lbs. of torque at the front axle. R.{Sir Henry Royce} | ||