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).
Speedometer calibration calculations for a Bentley 3 1/2 Litre chassis.
| Identifier | ExFiles\Box 165\4\ img160 | |
| Date | 7th June 1933 | |
| RM{William Robotham - Chief Engineer} Y6065 BENTLEY 3 1/2 LITRE CHASSIS SPEEDOMETER CALIBRATION Effective tyre circumference (found by actual trial) 90.375" with India tyres 35 lbs per sq.in. 89.375" " Goodyear " 35 " " " Therefore wheel revs per mile = 1760 x 36 / 90.375 or 89.375 = 701.1 for India tyres. 709.0 for Goodyear tyres. Assuming an axle ratio of 10/41 Prop. shaft revs per mile = 2870 India 2907 Goodyear. Gear ratio prop shaft to speedo drive = 2/16 x 20/9 Hence speedo drive revs per mile = 797 for India tyres 807 for Goodyear tyres. 11/41 axle ______ 724 India tyres 734 Goodyear " 11/43 axle ______ 759 India tyres 762 Goodyear " Hs{Lord Ernest Hives - Chair}/Wst. 7.6.33 | ||