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).
Recalibration of Wraith speedometers due to a change in tyre radius.
| Identifier | ExFiles\Box 165\2\ img096 | |
| Date | 25th June 1937 | |
| To HPS{Horace Percy Smith - Experimental Factory Mgr}/CEE. c. to WST/CAP. 6051 Rm{William Robotham - Chief Engineer}/Wst.4/JH.25.6.37. Wraith Speedometers. Owing to an alteration in the static effective radius of the tyres, it has become necessary to revise the calibration of Wraith speedometers. The new calibration value of revs. per mile is 776, as compared with the present value of 772 revs/mile. We have three speedometers which should be returned for re-calibration, the first of which is intrument No.S.807. Will you please have this speedometer returned to be made right for 776 revs. per mile. At the same time it should be pointed out that this instrument was found to be 5.5% fast at 30 m.p.h. 7% fast at 60 m.p.h. and nearly 9% fast at 90 m.p.h. whereas we expect them to be accurate at 30 m.p.h. Rm{William Robotham - Chief Engineer}/Wst. | ||