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 the various causes of vehicle skidding, with a focus on uneven wheel pressure resulting from centrifugal forces.
| Identifier | ExFiles\Box 15\6\ Scan154 | |
| Date | 1st January 1931 guessed | |
| -2- This brings us to the next point. How did uneven surface grip or braking arise? The road grip of every wheel depends on:- 1) The proportion of load carried by it. 2) The grip of its tyres. 3) The grip of the road surface at the particular point. The braking of any particular wheel depends on the amount of braking power applied to that wheel. The braking powers applied to the rear wheels are only uneven when inaccurately adjusted. This ideal adjustment rarely, if ever, exists. Generally speaking the application is much heavier on one wheel that the others. Theoretically, therefore, we have arrived at four possible causes of skidding:- 1) Uneven wheel pressure. 2) Uneven wear of tyres. 3) Difference in the road surface. 4) Uneven application of the brakes. In practice, however, we need only consider the first cause - "uneven wheel pressure" - the other three, which are not serious causes of skidding, as they can be adjusted by other means, we shall revert to later. In examining the causes of unequal wheel pressure we find that, even when the load is equally distributed, as the result of centrifugal forces this always happens, as, for example, when taking a bend or in a sudden swerve, and, in fact, to a greater or lesser degree with every change in direction, even of the shortest duration. These centrifugal forces cause the body and load to roll to one side (the outer side of the curve), and when suddenly developed, as in a sudden swerve to avoid an obstacle, they become highly dangerous. The resulting tip momentum throws the whole weight for a time on the outer wheel while the inner wheel is relieved of all load or even lifted off the ground. The danger of skidding, therefore, exists whenever direction is changed, whether that change be voluntary or involuntary. But we have seen that skidding itself is a change of direction which means that every skid is a cause of other and possibly more serious skids. That is the reason why the causes of skids numbered 2, 3 and 4 above, about which we have said nothing so far, and which in themselves can be quite harmless, can become dangerous. A skid produced by these causes results, it is true, in a very small change of direction which in itself is of no importance. As this change of direction is very sudden it develops for a moment considerable centrifugal forces which, in their turn, give rise to Cause 1, uneven wheel pressure, and a secondary skid is thereby produced, which can easily assume dangerous proportions. This chain of circumstances, which appears perhaps involved, can be more clearly shown by the following table of causes:- | ||