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).
Confidential memo discussing speedometer accuracy in relation to tyre diameter changes at high speeds.
| Identifier | ExFiles\Box 59\2\ Scan058 | |
| Date | 21th August 1930 | |
| X4038. PN.{Mr Northey}3/WT21.8.30. S/W. Hs.{Lord Ernest Hives - Chair}..from PN.{Mr Northey} Copy to C. Confidential. Speedometers. Referring to your Hs{Lord Ernest Hives - Chair}/RM{William Robotham - Chief Engineer}2/AM.4.8.30. do you expect the speedometer to behave as if it were geared about 2% higher when the car is running at say 60/70 m.p.h., owing to the apparent increase in effective tyre diameter at such speeds, because if this is so this ought to be taken into account with the speedometer people. The arrangement as understood by them so far, was that the mileage should be as near accurate as possible, and that never at any time should the speedometers read greater than 5% fast, in order to make good any contingency of their being on the wrong side. PN.{Mr Northey} | ||