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 inaccuracy of road test performance curves published in motor papers due to unreliable speedometers.
| Identifier | ExFiles\Box 73\3\ scan0290 | |
| Date | 21th March 1925 | |
| R.R. 493A (50H) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. Expl. No. REF: Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}1/LG21.3.25. ROAD TESTS REPORTED IN - 'THE MOTOR' AND 'THE AUTO CAR'. Recently the motor papers have taken it upon themselves to publish curves of car acceleration and braking performance. Previously, these said papers have confined themselves to verbal descriptions interspersed with a few speedometer readings taken when climbing well-known hills. These curves purport to give the public accurate information by means of which they can discriminate between the qualities of various cars. We are convinced by a number of the results that we have examined, that the curves given are frequently inaccurate. We have no idea as to how the tests are carried out and whether they are the result of both way readings, but apparently the results depend almost entirely upon the accuracy of the speedometer. There are a number of speedometers on the market all of which have different characteristics; it is quite possible for one of these to be correct up to 50 m.p.h. and after that to read 15% fast at 70 m.p.h. It is most difficult to check a speedometer above 50 m.p.h. on the road. In our tests, if we wish to compare with accuracy the performance of two of our cars, we use the same speedometer on each. We have, however, mxxxx almost given up using the speedometer as a means of conducting technical tests. We are of the opinion that 'Brooklands' is about the only place contd :- | ||