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).
Effects of different axle ratios and carburetters on the acceleration and maximum speed of the Phantom model.
| Identifier | ExFiles\Box 19\1\ Scan297 | |
| Date | 6th November 1933 | |
| X7120 To PN.{Mr Northey} From Hs{Lord Ernest Hives - Chair}/RM.{William Robotham - Chief Engineer} c. SG.{Arthur F. Sidgreaves - MD} c. C. c. Wor.{Arthur Wormald - General Works Manager} c. KP. c. CX.{Major Len W. Cox - Advertising Manager} Hs{Lord Ernest Hives - Chair}/Ref: 7/KT, 6.11.33. X7121 40/50 ACCELERATION. Referring to PN.{Mr Northey}2/WT2,11.33. We should like to separate two points mentioned in your memo - i.e. Acceleration & Maximum Speed. MAXIMUM SPEED. Taking Maximum Speed first, there is no doubt whatever that the Phantoms with the new carburetters are on the average about 6 M.P.H. faster than those with the old carburetter. We are quoting Brooklands lap speeds which are the only reliable figures. Hs{Lord Ernest Hives - Chair}/Lid.{A. J. Lidsey}1/KT.3.3.33. etc. We are certain that KP's and J.L.B's records of production cars will confirm this. ACCELERATION. The 12 x 41 axle ratio with 19" wheels gives a 6% higher ratio than the 11 x 41 axle ratio and 20" wheels. Up to 40 M.P.H. on top we anticipate that this will cancel the advantage of the new carburetter and camshaft. However, the characteristics of the latest Phantom engine were specifically evolved, as on the 20/25, to go with the synchromesh gearbox, and we submit that there is no comparison between the acceleration in 3rd. of to-day and 30-MY at speeds normally used on the road. Anyone who will not use the silent easy change third for acceleration is not reasonable. The higher axle was adopted to reduce fuss on direct drive and to ease the work of the engine. The only available means of improving the top gear acceleration at the present moment is to revert to the 11 x 41 axle, retaining the 19" wheels. Our main objection to this is that under exceptionally favourable conditions it might be possible to over rev. the engine. However, with this low axle ratio, we shall not be in an appreciably worse position relatively than we are at present on the 20/25. | ||