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).
Performance comparison and analysis of gear ratios and engine capabilities for different vehicles.
| Identifier | Morton\M21\ img079 | |
| Date | 27th June 1921 | |
| To R.{Sir Henry Royce} from DA.{Bernard Day - Chassis Design} -5- DA{Bernard Day - Chassis Design}5/G27/6/21 Contd. (a) The Austrain Trials cars with 4500 lbs. and wheels 33.2" dia. would climb 1 in 3 Then M.E.P. = 63.8 lbs. ins. sq. (shewing this performance to be easy) (b) With 3 tons 10 cwts. (7840 lbs) our standard car will stall on a gradient of 1 in 4 (34" wheels) Then M.E.P. = 87 lbs. ins. sq. (shewing that the performance is impossible.) (7) The maximum weights our standard car will carry up 1 in 4 are - Low compression - 6620 lbs. High compression - 6840 lbs. 34" wheels. (8) The 30 cwt. Crossley lorry (engine 4.5 x 5.5 x 4)cyls. believed 38" wheels, 1st gear ratio 20.47) took 3 tons 12 cwts. (8064 lbs) up in 1 4. Then M.E.P. = 73.3 lbs. ins. sq. (shewing the engine to be slightly inferior to the R.R.) (9) With 73.5 M.E.P. to take 9688 lbs. up 1 in 4 we require a gear ratio of 18.92, which may be obtained by altering constant mesh wheels from 75/45 to 80/40, and the 1st speed sliding wheels from 47/23 to 48/22, both of which are possible. (handwritten: axle ratio from 57/14 to 52/12) The effect on the ratios is as follows - 4th speed. 3rd. 2nd. 1st. 4.33 6.45 (struck through) 7.72 9.63 (struck through) 11.55 18.92 (10) Comparing this with the Crossley the capacity per lb. of load per revolution if the road wheel is - Crossley - 890 cu. incs. Rolls-Royce - 886 (struck through) 878 cu. incs. The difference being explained by the Rolls-Royce being slightly the better engine. (11) From the above it is evident that the whole trouble lies in the gear ratio, though the performance of the car would be improved (according to the information given on the power curves) by using high compression pistons. DA.{Bernard Day - Chassis Design} | ||