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).
Calculating car speeds in MPH for different axle ratios, based on speedometer and road wheel revolutions.
| Identifier | ExFiles\Box 165\4\ img014 | |
| Date | 8th March 1928 guessed | |
| Speedometer Revs. .3511 of propeller shaft revs. At. 600 Speedometer Revs/Min. Car Speeds are 17 x 52 Axle ratio 33. M.P.H. 16 x 52 Axle " 31. M.P.H 15 x 52 Axle " 29.3 M.P.H Road wheel revs/mile with present standard tyres 33 x 6.75- at 35 lbs | []" pressure, 625. | ||