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).
The required speedometer calibration based on the effective circumference of new tyres.
| Identifier | ExFiles\Box 165\2\ img186 | |
| Date | 15th December 1938 | |
| To By/RD. 6065 Rm{William Robotham - Chief Engineer}/RC.{R. Childs}6/JH.15.12.38. We have now obtained the effective static circumference of the 16" x 7.0" tyres which are to be used on 2.B.50, and find that the effective circumference at 30 m.p.h. is 92.4". The required calibration for the speedometer will therefore be 705 revs/mile. Rm{William Robotham - Chief Engineer}/RC.{R. Childs} | ||