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).
Analysis of wheel and speedometer revolutions per mile for Dunlop 'Fort' 650 x 16 tyres on a B.V. model with a 10/43 axle ratio.
| Identifier | ExFiles\Box 165\2\ img334 | |
| Date | 1st August 1941 guessed | |
| -2- tyres when used on the B.V. using a 10/43 axle ratio. Dunlop, 4 ply, "Fort" 650 x 16 tyres True Speed | Wheel Rev/Mile (Cold, Hot) | Speedo Rev/Mile. (Cold, Hot) 30: 726, 721, 780, 775 40: 723, 718, 777, 772 50: 720, 715, 774, 768 60: 716, 711, 770, 765 70: 714, 708, 767, 762 80: 710, 705, 763, 758 90: 707, 702, 760, 755 Dunlop, 6 ply, "Fort" 650 x 16 tyres True Speed | Wheel Rev/Mile (Cold, Hot) | Speedo Rev/Mile. (Cold, Hot) 30: 727, 722, 781, 776 40: 724, 719, 778, 773 50: 720, 715, 774, 769 60: 716, 711, 770, 765 70: 713, 708, 766, 761 80: 709, 704, 762, 757 90: 705, 700, 758, 753 Thus, the speedo drive rev/mile at a speed of 30 m.p.h., varies from 775 to 781, taking both tyres into consideration. A mean value of 778 seems to be the best value to work on, for the above conditions. The above takes into account a 1% increase in tyre radius which very nearly agreed with the actual loss at 30 m.p.h. We assume that the tyre loss above 30 m.p.h., may be accounted for by dial correction, and since any additional correction will be above the "30" mark, we shall have the same accuracy at 30 m.p.h., as before. The existing specification gives a correction on the dial of 3 m.p.h., at a speed of 90 m.p.h., and on top of this a plus two limit throughout the range. -Continued- | ||