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).
Issues with speedometer accuracy and performance readings during continental trials.
| Identifier | ExFiles\Box 19\1\ Scan098 | |
| Date | 2nd April 1931 | |
| HS{Lord Ernest Hives - Chair} 87120. E.R./L.T.C.2.4.31. 26-H.P. Continental Trials. At the present moment there is a troublesome obscurity in respect of the present speedometer and its characteristics, now fitted to this car. After much collaboration with EFC. and By.{R.W. Bailey - Chief Engineer} a scheme has been arrived at with our old gear, whereby the miles run indicated by speedometers will be reasonably accurate, (I believe within .7 of 1%), and the speed indication will be accurate within 5% at all speeds, this being an optimum reading, taking into account as far as feasible, the various influences tending to affect the reading, such as temperature changes of the instrument, varying diameters of driving tyres at various speeds and pressures. In achieving these results fully, it was realised that a compressed scale would be necessary, that is one in which the graduations would not be evenly spaced, and instructions have been given to the A.T. people to this effect. It appears that early in January EP.{G. Eric Platford - Chief Quality Engineer} asked that the speedometer then fitted to this car should be sent to him for examination, I conclude in order that he might make sure that it did not vary unduly from some speedometers fitted to other models coming through, and it was returned to us as instructed, by the 27th January, refitted to our car which was then out of Barkers' hands. After that date, whilst we had no reason to think that the actual performance of the car had fallen off, it was found that its maximum speed, instead of being as shown by the speedometer at say 95 m.p.h. would be 85 instead, a drop of over 10%. It has been most embarrassing for this car to give demonstrations to people under these changed conditions, most of whom of course have heard of the alleged performance either from friends or in the Press. So far no information exists as to where the change, or why the change was made. I am not questioning the wisdom of any change being made to this speedometer (if this was done) provided that it was done with our approval, and on specific instructions from us, and I should be glad to have any early possible information on this point. | ||