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).
Analysing car performance with a high axle ratio and high compression engine.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan225 | |
| Date | 30th November 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. -3- Expl. No. REF: Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/LG30.11.25. performance due to a high axle ratio and high compression engine. On direct drive, owing to the 17-tooth axle fitted to the sports car, its acceleration at low speed s suffers. The 17-tooth axle was fitted purely to enable the car to get to 90 m.p.h. with the reduced wind resistance. It is possible however to convert curve 'A' to [overtyped text] acceleration with a 15-tooth axle. This is done in - Graph V1. This shews quite clearly why a car is not normally geared for maximum speed. If it were the loss in low speed, acceleration would be very considerable - the gain in maximum speed almost negligible (See car performance). These particular curves, however, flatter the low geared axle because a high compression engine was used which maintained its power well at high r.p.m. and the car had not a stream-line body, so that wind resistance prevented any large gain in speed from a higher gear ratio. It is nevertheless an excellent example of a 15 v.{VIENNA} a 17-tooth axle. The increased performance given by the 15-tooth axle is paid for chiefly by :- (a) Wear and tear. This is greater than the 13% rise in axle ratio because at high engine speeds wear is not proportional to increase in r.p.m. (b) Petrol consumption. Graph Vlll. Shews the gain due to the higher compression ratio and reduction in weight. The latter being small, it is apparent that the high compression engine is responsible for the majority contd:- | ||