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).
Continued document discussing calculations for speedometer instrument revolutions per mile.
| Identifier | WestWitteringFiles\U\August1930-November1930\ Scan038 | |
| Date | 13th September 1930 | |
| -2- EFC2/A13.9.30 contd. compared with those at slow and moderate speeds. This result is presumably for fully inflated tyres. With lower inflation the effect would probably be greater correspondingly with (2), being less at high speeds. It will be seen from the above that the fixing of the speedometer instrument revolutions per counter mile cannot be done with any degree of certainty, as the maximum number of speedometer drive revolutions per car mile occurring with the smallest size of tyres used only partly inflated and at slow speed may differ as much as 7½% from the absolute minimum number of drive revolutions per car mile occurring with the largest size of tyres most highly inflated and at high speeds. It is only possible to make a suitable compromise. The absolute minimum number of road wheel revolutions per car mile in the case cited is 595 - 2½% {vide (3)} = 580 but as this only occurs at high speeds perhaps only 1% or slightly less should be deducted giving the figure 590. 590 road wheel revolutions per mile corresponds to speedometer drive revolutions per mile of 590 x 41/11 x 2/18 x 26/8 = 794 This figure 794 therefore, would appear to be a suitable figure with which the instrument spindle revolutions per | ||