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 adjustments and variations in tyre circumference figures.
Identifier | ExFiles\Box 50\4\ Scan170 | |
Date | 2nd March 1928 | |
EFC. {E. Fowler Clarke - Electrical Engineer} V4308 2.3.28. B 156 SPEEDOMETER B.156. 765. 16/52. We do not think it worth while to attempt to gain the .9 m.p.h. at 600 r.p.m. on this speedometer by remagnetising it. We are already 8.5% fast; our original requirement was 10% but in view of the fact that we cannot obtain the last 1½% by means of the adjustment provided, we shall be satisfied with it as it is. My figure of 60 m.p.h. at 700 r.p.m. of the driving spindle is correct for a 16/52 axle fitted with 33 x 6.75 tyres which have an effective running circumference of 103.25". There has been considerable variation; in this latter figure recently, but now it has been definitely fixed that the circumference figure to be taken as correct for these tyres is 103.25". This may explain why my figure did not agree with other figures you have received. I have recently gone into this matter with the D.O. having found that the figures given on the drawings were incorrect and misleading, these are now being corrected. A.J.Lidsey. | ||