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).
Analysis of speedometer and odometer accuracy based on tyre size, inflation, speed, and temperature.
| Identifier | WestWitteringFiles\U\August1930-November1930\ Scan039 | |
| Date | 4th September 1930 | |
| -3- EFC2/AD4.9.30 contd. counter mile should be made to agree. The resulting slight negative error in the counter mile in the extreme circumstances of the largest tyres used most highly inflated and at the highest speeds might be allowable because the average circumstances of running either (a) with smaller tyres (b) with lower inflation or (c) At more moderate speeds would tend to correct this error. and render it somewhat positive on the average. N.B. This is a slightly different aspect of the matter than given in our EFC1/AD19.8.30 in which we suggested that the bias might be slightly in the other direction. We are now of the opinion that that would make the positive error of the mile counter too large on the average. In regard to the speed indicator portion of the instrument we are of the opinion that this should be made to agree with the counter miles at speeds up to say 40 miles per hour when the instrument is at a temperature of 35°C. If the instrument spindle revolutions per minute are represented by N and its revolutions per counter mile by M the correct (internal) reading in miles per hour should be 60 N / M Over the range of speeds up to 40 miles per hour the reading, on the average, will therefore be on the high side to the extent that the counter miles are reading high on the average for reasons already mentioned, and at lower temperatures the speed readings will be relatively | ||