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 accuracy and calibration for the 20/25 Chassis U Series.
| Identifier | ExFiles\Box 59\2\ Scan154 | |
| Date | 23th May 1932 | |
| X60516 By.{R.W. Bailey - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. c. to E.{Mr Elliott - Chief Engineer} c. to MX.{John H Maddocks - Chief Proving Officer} c. to EP.{G. Eric Platford - Chief Quality Engineer} Hs{Lord Ernest Hives - Chair}/Wst.2/MA.23. 5. 32. SPEEDOMETERS ON 20/25 CHASSIS U SERIES. According to our calculations which we confirmed by road tests on 19-64 the revolutions per mile figure for speedometers now being fitted to U series 20/25 chassis are too low. 810 revs per mile is the D.O. figure for these whereas our calculations shew this to be 838. Actual road tests taking the average readings using new and worn tyres gave a figure of 842. Production speedometers therefore, on the assumption that our actual recorded figures are correct, will read 4% fast on the mileage recorder which is very undesirable. Also as the A.T. Co., already make the speedometer read about 3 to 4% fast (Cold) to allow for the temperature effect, the m.p.h. reading may be anything from 6 to 8% fast. We consider the m.p.h. reading should not read more than 5% fast as we understand customers notice this and complain accordingly. The mileage recorder should if possible read correct miles to within +- 1%. Hs{Lord Ernest Hives - Chair}/Wst. | ||