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 calibration adjustments due to a change in wheel and tyre circumference, with recommendations.
| Identifier | ExFiles\Box 165\2\ img303 | |
| Date | 1st January 1941 | |
| Rm{William Robotham - Chief Engineer}/GB.2/ET.1.1.41. - S - The revs per mile for a wheel with 80.5" circum- ference, as used up to now, is 787. The error in the fifth wheel was therefore 787 - 746 --------- = 5.2% slow. 787 The results on the tests carried ou t up to this stage may be corrected accordingly. A new wheel and tyre has now been fitted. Its circumference was measured by rolling it along the shop floor and was 81". The speedometer dial was recalibrated to suit this, as follows:- 10 m.p.h. - 130 r.p.m. 50 m.p.h. - 652 r.p.m. 20 " - 261 " 60 " - 782 " 30 " - 391 " 70 " - 913 " 40 " - 522 " 80 " - 1043 * " RECOMMENDATIONS. 1. The wheel circumference should be checked before each test and, if possible, the tyre pressure ad- justed to give a circumference of 81". 2. When the above is not possible owing to tyre wear or stretch, the dial should be re-calibrated, using an accurate Hasler. Rm{William Robotham - Chief Engineer}/GB. | ||