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 steering dynamics, roll, and tyre pressure effects from test data.
| Identifier | ExFiles\Box 170\3\ img140 | |
| Date | 29th December 1937 | |
| Mr. Grylls, Rolls Royce Limited, Derby. 29. 12. 37. The steering angle, less Ackermann, is the difference between front slip angle and attitude curves. So that front slip crosses steering angle where rear slip crosses Ackermann. This is the point where the centre of turn is in line with the front wheels. Roll angle against G is a straight line unless rubber bump or rebound stops or other rate variations come into play. Note that loading and tyre pressure are stated on the charts. The tyre pressure quoted, and carefully controlled during the test, is 3 lbs above the cold inflation pressure, front and rear, that is Oldsmobile's inflation is 25,28 cold, so car maker's inflation test is run at 28 and 31. The tyre makers inflation test is 3 lbs above the Tyre & Rim Associations cold inflation for the actual loads on the car (Dont pay any attention to the SMMT inflation figures. They appear to us to be quite wrong.) On your charts, the first is typical of rear stabiliser cars, but much more moderate than say a 1936 Olds 8. Second chart shows in curve 1 the typical effect of increased understeer from increased roll. Curve 2 with its final dip down (rear skid) shows that even without the stabilizer too much of the roll couple is carried on the rear tyres. Even more so with ballasted rear in curve 3. Fourth chart showing front stabilizer results shows a desirable amount of understeer at .4g. Greater figures for steering wheel angle can only be explained by seeing the front slip angle. When this exceeds about 6 degrees one can expect to see the steering wheel torque and so the steering wheel angle curve, reach the maximum and begin to fall off. The increase in the steering wheel angle curve is of course due to elasticity in the steering linkage. Effect of hollow-faced banking is that the car will run round the banking, in the "natural" lane for its particular speed in the true Ackermann position, i.e. centre of turn in line with rear wheels. Driving fast in a low lane brings into play forces similar to those on a flat turn and shows results plotted against G very similar to those on the skid pad. We think these results tend -2- | ||