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).
Letter explaining the detrimental effects of tyre pressure reduction on performance and life, with reference to two graphs.
| Identifier | ExFiles\Box 39\2\ Scan159 | |
| Date | 22th December 1922 | |
| Messrs. Rolls-Royce Ltd. December 22nd.1922 In order to show you how important the effect of pressure reduction is on the performance of the tyres we are enclosing you herewith two graphs. That marked "A" shews the deterioration in the tyre performance due to pressure reduction. It is expressed in percentages. The figure 100 on the abscissae represents the tyre life, and the figure 100 upon the ordinate represents the normal pressure to give that life. The load is constant in all cases. It should be understood that this curve represents the deterioration due solely to fatigue of the cotton composing the casing, but there is a second factor which has a very important bearing upon the tyre performance, and which cannot be shown in this curve. We refer to the relative liability of a cover at different inflation pressures to fracture under impact blows, due to severe local flexing. This is shewn on curve "B", and it should be noted that this is taken on a new cover in which of course the cotton was not fatigued by previous running at low pressure. Curve "B" therefore represents the liability of a new cover to fracture due to impact at different pressures. This is expressed in percentage also, and the lowest liability shown on the abscissae is taken as 100; the pressure being shown on the ordinates. You will notice here that the liability of an unfatigued cover to be fractured by a blow is at its lowest when the inflation pressure is about 50% greater than that for which we ask in our schedule, and that from the point of least liability, the curve is exceedingly steep. You will appreciate, however, that this leads to a third factor not shewn by these two curves - viz., that the liability to fracture by impact becomes considerably greater as the fatigue of the cotton increases by low pressure running. As a result of all these factors, reduction of tyre life proceeds in a ratio greatly exceeding the pressure reduction. It is for these main reasons that at the present time we feel that we would not be well advised to make any recommendations -2- | ||