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).
20 HP axle ratios and the effect of different tyre sizes.
| Identifier | ExFiles\Box 58\1\ Scan045 | |
| Date | 19th May 1928 | |
| X5820 To CWB. from Hs.{Lord Ernest Hives - Chair} Hs{Lord Ernest Hives - Chair}1/LG19.5.28. 20 HP. AXLE RATIOS. V5350 The effective rolling circumferences of the 31 X 5.25 and 31 X 6" tyres at 35 lbs/sq.in. are :- 31 X 6 100" 31 X 5.25 97.5" However, due to its larger section, the 6" tyre can, without danger, be run at 5 lbs/sq.in. lower pressure when its effective circumference becomes 99.5". Therefore we may say that at present the gear ratio of the car will be altered 2% by fitting the 6" tyre. The old 11 X 50 axle gives a ratio of 4.55 - 1 The new 10 X 47 " " " " " 4.7 - 1 Therefore with the new axle the gear ratio will be lowered 3.3%, or by fitting the 10 X 47 axle and 6" tyres the gear ratio will be 1.3% lower than the present 11 X 50 axle with 5.25" tyres. Hs.{Lord Ernest Hives - Chair} | ||