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).
Calculations for speedometer revolutions per mile based on tyre diameter.
| Identifier | ExFiles\Box 50\4\ Scan021 | |
| Date | 13th March 1928 guessed | |
| 3.1416 34 ______ 125664 94248 ______ 106.8144 Circumference of Road Wheels. 106.8) 63360 (593.3 Revs of Road Wheels. 5340 ---- 9960 9612 ---- 3480 3204 ---- 2760 593 x 60/13 x 15/4 = 35580/13 = 684 (Note: In the calculation, '60' and '4' are struck through, with '15' written above '60') 650 13)35580(2 684 revs (670) revs With 34" tyres Speedometer will turn 684 revs for every mile of car travel - If Speedometer turns 670 revs per mile the tyres should be 34.8" in dia in order that Speedometer should register correctly - 684 13 x 60 636 14 x 60 | ||