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).
Customer complaints about fast-reading speedometers on the Phantom II, detailing test results for different calibrations.
| Identifier | ExFiles\Box 59\2\ Scan039 | |
| Date | 23th June 1930 | |
| [STAMP] By G Mot c Hs{Lord Ernest Hives - Chair} o Hs{Lord Ernest Hives - Chair} [STAMP] RECEIVED JUN 23 1930 [HANDWRITTEN] X4308. [TYPED] Mx{John H Maddocks - Chief Proving Officer}3/T23.6.30. re Speedometer - Phantom ll I understand from EP{G. Eric Platford - Chief Quality Engineer} that numbers of customers are complaining that their speedometers read fast, and they are going to the A.T. people who are exchanging their speedometers and fitting one-of 810 r.p.m. instruments. At the commencement of Phantom II programme we fitted approximately 130 similar speedometers - we then fitted a number of 765 speedometers, and we have lately changed to a 785. I know we appreciate that the 765 gave a much too high reading, and I understand that the instrument complained of is the one we are now fitting as standard i.e. 785, and as there appear to be various estimates of the percentage that this instrument was reading fast, we have carried out some special careful tests on chassis. We carried out tests with a chassis fitted with new Dunlop Silent Tread Tyres 20 x 7 on 20" wheels at a pressure of 40 lbs per square inch, with a car weight of 47 cwt. We found the wheel revolutions per mile under these conditions to be 615, giving a speedometer shaft speed of 828 revs. per mile. Therefore, a standard speedometer of 785 revs. per mile reads 5¼% fast, this of course will increase with tyre wear or lower pressures. It therefore appears that the speedometer makers procedure in cases of complaint of fitting an instrument calibrated for 810 revs. per mile gives a more accurate reading, although even this would be a few per cent fast. We are satisfied that as an instrument the 785 speedometers supplied are within limits laid down. MX{John H Maddocks - Chief Proving Officer} [SIGNATURE] | ||