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).
Experimental three-speed gearbox ratios for the 25-30 model, comparing performance with other vehicles.
| Identifier | ExFiles\Box 104\4\ scan0267 | |
| Date | 18th March 1936 | |
| x528 GRY.{Shadwell Grylls} Your Comments please Rm.{William Robotham - Chief Engineer} C.E. Des. LIS. KHC. HS{Lord Ernest Hives - Chair}/RW. E/HDY.{William Hardy}2/HP.18.3.36 Experimental Ratios for Three Speeds for the 25-30 Gearbox. We send herewith N.Sch.4783 which shows the ratios we propose. 1st speed is made .35 instead of the standard .3, and 2nd speed is .67 with a lower ratio .64 available by the use of the standard 3rd speed gears. The standard 25/30 3rd speed is .73. We attach tabulated data relating to this question, and it will be seen that we calculate that fully laden the car will climb 1 in 3.2 in 1st, 1 in 6.4 in the high 2nd, and 1 in 6.0 in the low 2nd. Corresponding figures for the 20/25 with the standard ratios are 1st 1 in 3.2, 2nd 1 in 5.2, 3rd 1 in 8.3. Maximum effective speeds are for the three speeds 1st 28 m.p.h. high 2nd 47 m.p.h. and low 2nd 45.5 Standard ratios give 1st 22, 2nd 35 & 3rd 49. Above these speeds more acceleration is obtained in the higher gear. At 4,000 r.p.m. the high and low 2nds give 53 & 51 and the standard 3rd 58. In all cases the laden weights are with 4 persons in the car (5 1/2 cwts allowed) and 1 cwt. of luggage, making with a 39 cwt car a total of 45 1/2 cwts. This is of course not the maximum weight that can be taken on the cars, but we prefer to take what might be called a normal figure. All cars are assumed to have a B.M.E.P. of 105 at 1000 r.p.m. except the Bentley for which 115 lbs sq.in.is allowed. It will be seen that the 25/30 power weight ratio is inferior to that of the American cars quoted, and it is for this reason that the climbing ability in 2nd speed is inferior in our case. The Phantom III by comparison is excellent and by reason of the high bottom gear that should be allowable in this case should be very well able to standard the loss of a speed. E/HDY.{William Hardy} | ||