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).
Summary of fuel consumption and performance tests comparing Napier, Silver Ghost, and Silver Rogue cars, with calculations for windage effects.
| Identifier | ExFiles\Box 20\6\ Scan015 | |
| Date | 25th October 1911 | |
| (3) PFRS. No. 527. 25.10.11 (Sheet 3 of 3) Time taken to consume one gallon on the road, at 20 m.p.h. is about one hour. Therefore, the horse power absorbed (one H.P.) by the extra windage area (9.85 sq. ft.) at 20 m.p.h. represents very roughly .092 galls. of petrol per hr. If windage of Silver Rogue had been cut down at 10.4 sq. ft. the consumption would have been reduced to about 22.1 m.{Mr Moon / Mr Moore} per gall. or 45 ton miles per gallon. SUMMARY. Car. Miles per gall. Ton miles per gall. Distance run Speed at 1000rpm. Windage. Napier 19.85 42.57 799 ms. 37 1/4 mph. 10.4 sq. ft. Silver Ghost 20.8 40.8 420 37.88 Silver Ghost 23.25 45.8 46 1/4 37.88 Silver Rogue 20.1 40.98 2000 39.46 19 3/4 Silver Rogue corrected for windage. 22.1 45 2000 39.46 10.4 ---------------------- | ||