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).
Recommendation for varying back axle gear ratios in proportion to car weight to improve performance.
| Identifier | ExFiles\Box 49\1\ Scan227 | |
| Date | 12th October 1920 | |
| Contd. -2- R18/G12.10.20. Now at present we are giving a larger ratio of back axle gear, and you will remember that I particularly recommend that the still lower gear should be made standard for the heavier cars. I now find that in going very deeply into this question none of have realised how important it is to still further increase the back axle gear ratio on the heavy cars. Providing we wanted equal acceleration, and equal hill climbing on all the cars the back axle ratio should increase in proportion to the weight. Below is a list of what I should recommend:- (1) 3.25 to 1 gear ratio for cars up to 2.25 tons. 3.5 to 1 " " " " from 2.25 to 2.5 tons. 3.75 to 1 " " " " from 2.5 to 2.75tons. 4 to 1 " " " " from 2.75 to 3 tons. Supposing that we had the same gear box for all these cars, they would all go up the same maximum grade, which we think should be a 25% grade, namely, 1 in 4. You will see from this that we have never varied the back axle, ratio anything like the amount we ought to have done, principally on account of the difficulties anticipated of getting silent gears; we must not let this disadvantage rule us without a great effort. Now it has been ruled out by yourself and the Works, that it would not pay to make a three speed box standard for the present chassis so we have only to consider our new work. Contd. | ||