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).
Calibration and accuracy issues of Bensport speedometers.
| Identifier | ExFiles\Box 165\4\ img181 | |
| Date | 5th March 1933 | |
| X1807 By/CGH.{W Clough} From Hs{Lord Ernest Hives - Chair}/Wst. c. to By/RD. c. to E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} Hs{Lord Ernest Hives - Chair}/Wst.7/MA.5.3.33. BENSPORT SPEEDOMETERS. The Bensport speedometer revs per mile figures as given on the drawing do not agree with actual measurements which we have now been able to obtain on the road and on the dynamometer. The drawing figures are:- 11/41 axle. 18 x 5.50 tyres. 750 revs per mile. 11/43 " 18 x 5.50 " 785 " " " 10/41 " 18 x 5.50 " 825 " " " our figures, which we have confirmed in the case of the 11/43 axle, are respectively:- 734, 762, and 807 revs per mile, consequently the instruments read slow and more so when the temperature rises on the instrument board, as it normally, does, to 30°C. The percentage is approximately 3% slow or 58 M.P.H. at 60 M.P.H. (actual). We consider it very important that the Bensport speedometer should not read slow or less than 3% fast (in order to account for the temperature effect). The usual unwritten law is for our speedometers to read 5% fast at full scale deflection and we certainly consider in the case of the demonstration Bensport chassis that this should be the case. The actual revs per mile figure of the instruments should be exact in order to avoid error in the mileage recorder and the reading made 5% fast by adjusting the scale which we understand the A.T.Co., can do fairly easily. Hs{Lord Ernest Hives - Chair}/Wst. | ||