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).
Analysis of vehicle roll stiffness and cornering forces for different spring layouts and tyre pressures on a Bentley III.
| Identifier | ExFiles\Box 100\2\ scan0015 | |
| Date | 15th October 1937 guessed | |
| -2- No experimental figures for the roll stiffness of a Bentley car were available, but from the figures for a Wraith car the added roll stiffness for front and rear springs in roll due to twisting of the spring were deduced, the assumptions made being that normal spring deflection is proportional to its length cubed and torsional deflection to its length, and the bending and torsional moments of inertia remain proportional to each other. From this, and a knowledge of the sprung and unsprung weights of the car, the weight transference front and rear were deduced for the given inward acceleration, and from the resulting load on each tyre expressed as a percentage of the rated load, cornering coefficients and hence cornering forces for the tyre shown in the accompanying graph were obtained. Knowing the actual outward forces front and rear, the corresponding slip angles were obtained, and the proportion of the difference of these to the actual oversteer provided by the tyres gave a ratio of slip for the 6.50-16.00 tyre and the one for which the curve was originally drawn. This ratio appeared to be slightly different for the two tyre pressures concerned but this may have been due to inaccuracies. These ratios were then used for the Bentley III, for which four cases were investigated. These are: 1. original rear spring layout and springs of 5" static deflection front and rear ( we believe this is as detailed) 2. "anti-shake" rear spring layout and springs of 5" static deflection front and rear. 3. original rear spring layout front springs 6.5" static deflection rear spring 5.5" static deflection. 4. "anti-shake" rear spring layout, front springs 6.5" static deflection, rear springs 5.5" static deflection. As a matter of interest, case (3) was investigated both for 30 lbs/sq.in. tyre pressure and 25 lbs/sq.in. tyre pressure, the other three cases being for 30 lbs/sq.in. only. The results are given in the accompanying table. | ||