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).
Phantom axle ratios and their effect on car performance.
| Identifier | ExFiles\Box 67\2\ scan0186 | |
| Date | 23th November 1925 | |
| EXPERIMENTAL REPORT. Expl. No. x8420 REF: HsS/LG23.11.25. To BJ. from Hs.{Lord Ernest Hives - Chair} c. to EY. PHANTOM AXLE RATIO. x8420 x8350 BJ2/H16.11.25. Axles with 14/52 ratio were tried on Experimental Phantom cars last year. Cars with heavy closed bodies were tried by Sales with 14/52 and 15/52 axles and they reported unfavourably on the low geared axle. Briefly the objections to the low geared axle are :- (1) More engine noise and fuss. (2) Increased petrol and oil consumption. (3) Increased water heating. (4) Increased wear on engine. With a car weighing 55 cwts., the present EAC. engine can surmount a gradient of 1 in 10.5 when driving through a 15 X 52 axle. If the axle ratio is altered to 14 X 52, the maximum surmountable gradient on top gear becomes 1 in 9.8. If, however, the car weight is reduced 3 cwts. to 52 cwts., the car will be able to climb a gradient of 1 in 9.8 with a 15 tooth axle. In other words, 3 cwts. off the body and chassis of the present car will give an improvement equal to that obtained by fitting a 14 tooth axle, on hill climbing and acceleration. With regard to maximum speed. Up to 70 m.p.h. practically no difference between the 14 and 15-tooth axle should be observed. At 75 m.p.h. however, with the lower geared axle, 8½% less road wheel H.P. is available to drive the car, hence contd :- | ||