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).
Petrol consumption in relation to various back axle gear ratios.
| Identifier | ExFiles\Box 39\2\ Scan201 | |
| Date | 3rd April 1919 | |
| To R.{Sir Henry Royce} from EH. c. to CJ. c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} X3542 COPY EHL/LG3.4.19 RE PETROL CONSUMPTION AND BACK AXLE RATIOS X.3457 - X.3071. 3056. With reference to Mr. Royce's memo R2/G28/3/19, we find that the only 4-cylinder car which we could carry out the tests suggested is at present all in pieces waiting for a new frame. As regards the spare rear axles with different gear ratios, these have been dismantled piecemeal in order to supply spare parts for repairs. Under these circumstances we would much prefer carrying out the tests on the 40/50 chassis. The back axle ratio we use at present on the 40/50 chassis is 3.25 to 1. We have other gears which will give us a ratio of 3.06 to 1, we also could fit in some old type gears which will give us a ratio of 2.95 to 1. Mr. Day has looked into the question of making a lower gear to fit into the present axle and finds that we could make a ratio of 3.46 to 1 and 3.71 to 1. We suggest trying the following ratios:- 3.06 to 1, 3.25 to 1 and 3.46 to 1 one standard 40/50 chassis. We have carried out a test on the road under identical conditions as regards road and speed and find that on the top gear we do 16 miles to the gallon. If we run on the third gear and maintain the same speed (35 M.P.H.), the consumption is 12 M.P.G. The mixture in each case was adjusted so as to be as weak as possible without mis-fires. Consumption tests we have taken lately have proved that different road and tyre conditions will make a difference in the M.P.G. of 16 1/2 to Contd. | ||