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).
Speedometer accuracy at high speed, affected by the centrifugal effect of tyres, and a proposal to correct it.
| Identifier | WestWitteringFiles\U\August1930-November1930\ Scan040 | |
| Date | 4th September 1930 | |
| EFC2/AD4.9.30 contd. -4- (to the miles) high, and absolutely, still higher. At the higher range of speeds (above 40 miles per hour) the effect is, (owing to the centrifugal effect of the tyres) that the drive revolutions per car mile become decreased, whence both the counted miles and the speed indications will tend to become more correct. They are only likely to become low in certain very extreme circumstances, the degree of likelihood depending upon the actual selection of the instrument revolutions per counter mile being greater or less than the 794 arrived at. It is at the higher speeds however, that we particularly want the speed indications to keep up and even read a little higher in proportion rather than lower due to the centrifugal effect of the tyres. At the same time we do not want to interfere with the mile counting to any extent. The only way of attaining the desired end would appear to be deliberately to compress the miles per hour scale progressively over 40 miles per hour onwards and render it disproportionate instead of being a proportional scale as at present. We suggest that the amount of this be worked out from the known data of the centrifugal force effect at different speeds and the requisite percentage contraction of the scale at various speed indications | ||