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 testing of A.T. speedometers on a Phantom II chassis, including temperature-related performance.
| Identifier | ExFiles\Box 50\4\ Scan332 | |
| Date | 22th November 1929 | |
| X4308 To By.{R.W. Bailey - Chief Engineer} from EFC. " Hs.{Lord Ernest Hives - Chair} " Wor.{Arthur Wormald - General Works Manager} EFCL/AD22.11.29. X.4308. A.T. SPEEDOMETERS ON PHANTOM II. Two up-to-date standard 765 revolution per mile instruments have been checked for gear ratio to counter and mile per hour readings at 600 r.p.m. exactly. One of these D467. 765. 11/41 was taken from production, the other is the one M189. 765. 11/41, recently allotted to Experimental Chassis 18-EX for R.{Sir Henry Royce} Both instruments were found to be correct in regard to the 765 spindle revolutions per counter mile. The speedometer drive revolutions per mile on the S.S. standard chassis fitted with standard tyres are 819, and in the extreme case of the largest tyres ever fitted 801. Mileages will therefore read 7.0% and 4.7% high in the two cases. The speed indications of D467. 765. 11/41 at 600 r.p.m. exactly with the correspondingly correct drive revolutions per mile were found to be :- | Temperature (°C) | Miles per hour indicated at 600 r.p.m. | Corresponding correct revs. per mile | |---|---|---| | 17.2 | 47.1 | 765 | | 21.0 | 46.5 | 775 | | 25.0 | 46.0 | 782 | | 28.0 | 45.8 | 786 | | 30.0 | 45.5 | 792 | | 32.0 | 45.0 | 800 | shewing the instrument to be correct in itself at 17.2°C. with an error of 3.4% at 30°C. The temperature error is reasonable, but we asked the makers to make these instruments internally correct at about 30°C. | ||