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).
The gear ratio limitations for the 20 HP model.
| Identifier | ExFiles\Box 6\4\ 04-page218 | |
| Date | 1st May 1929 | |
| X5310 E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}5/LGS.5.29. 20 HP. GEAR RATIO. X5310 X5820 With reference to E1/M26.4.29. We are not quite sure what figures you have used to arrive at the gear ratios you quote, but the standard tyres for the 20 HP. are now 6" Extra Heavy for 19" rims. + These tyres have a rolling circumference of 96" which with the standard axle ratio of 11 X 50 gives a road speed of 20 m.p.h. at 1000 eng.r.p.m. Therefore at 60 m.p.h. the engine is doing 3000 r.p.m. and as you will have noticed on 17-GLV the car shews a marked disinclination to go any faster. Even on 12-GLV with the larger valves, the induction pipe depression at 3000 revs. is such that the power is falling off rapidly. The road wheel dynamometer figures are rather optimistic in this respect. We therefore think we have about reached the limit of the gear ratio on the 20 HP. at present. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||