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).
The increase in tyre radius at various speeds based on road and machine tests.
| Identifier | ExFiles\Box 157\3\ scan0138 | |
| Date | 4th April 1941 | |
| Product Design Division, Fort Dunlop. WEH/FBJ/MT. 4th April 1941. INCREASE IN TYRE RADIUS AT VARIOUS SPEEDS A graph is attached giving the increase in running radius with speed of 6.50-16 4 & 6 ply tyres. Up to 75 mph., these were obtained on the road by measuring the number of revolutions the tyre made whilst covering a measured mile at a constant speed. Tests were also carried out on our high speed machine, and as these gave results of the same order, the shape of this curve was used as a basis for extending the curve obtained from road tests. Within the pressure range used (26 - 30 lbs/sq.in) the change in radius with speed was independent of the inflation pressure. In all the tests the inflation pressures were adjusted to a fixed value (e.g. 26 lbs/sq.in) before each run. In practice a tyre heats up in running with the result that the inflation pressure and radius increase, the exact amount depending on the speed and the length of the run. 4 lbs/sq.in. is probably an average increase for fast cars and this increases the radius .1". Thus the figures shown in the graph are true at the start of a run, but when the tyres become hot the increase in radius is about .1" more. F.B.J | ||