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).
Request for up-to-date data concerning A.T. speedometers, focusing on road wheel revolutions per mile under various conditions.
| Identifier | ExFiles\Box 59\2\ Scan073 | |
| Date | 12th September 1930 | |
| X4308. 12.9.30. X.4308. A.T. SPEEDOMETERS (40/50 and 20/25 HP) UP-TO-DATE DATA REQUIRED. (1) Figures of road wheel revolutions per mile of the various tyres used at slow or moderate speeds and with normal inflations. (2) Figures showing the effect of the degree of inflation on the road wheel revolutions per mile at slow or moderate speeds for one or two particular types of tyres in more common use. (3) For the same few typical types of tyres with normal inflation, curves showing the law of variation of the road wheel revolutions per mile with speed. N.B. It appears to have been demonstrated that the centrifugal force effect on the tyres increases their effective radii. Query - To what extent does the spin or slip of the wheels, resulting from the fact that the speedometer is driven from the driving wheels, counteract this effect? It seems likely that the varying nature of road surfaces has some effect but that probably this is of insufficient importance in the average cases to be taken into account. The use of revolution counters operated by one or both rear wheels is suggested. In the case of information under the heads (1) and (2) this would appear to be a reliable way of obtaining it. In the case, however, of the information coming under (3) it would appear to be necessary to have some means of throwing the counters in and out of action when passing the starting and finishing points of a measured mile. EFC. | ||