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 road wheel diameter and gear ratios.
| Identifier | ExFiles\Box 50\4\ Scan022 | |
| Date | 14th March 1920 guessed | |
| 34" Road Wheels - (dia) 106.8 Circumference of Road Wheels 593 1/4 Revs of Road Wheels per mile - 593.25 x 60/14 x 1/4 = 636 Speedometer revs. per mile. 7) 593.25 2) 84.75 42.37 593.25 635.62 If Speedo revs = 670 per mile Revs of 3rd Shaft per mile = 670 x 4 = 2680 Revs of Back Wheel per mile = 2680 x 14/60 = 625.3 Dia of Back Wheels = 63360 / (625.3 x 3.1416) = 32.2" 625.3 3.1416 37518 6253 25012 18759 1964.44248 1964.4) 63360 (32.2 58932 44280 39288 4992 In above & Back axle ratio is 14/60 Speedo Drive gear ratio 3/12 With above Speedometer at 670 revs.p.mile would register 5% low. if wheels are 34" dia | ||