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).
Road wheel horsepower comparison graph between a Humber Super Snipe and a Wraith 27 G VI.
| Identifier | ExFiles\Box 108\2\ scan0211 | |
| Date | 13th January 1939 | |
| B.H.P. ENGINE R.P.M. TABLE: ENGINE R.P.M. | M.P.H | HUMBER | WRAITH 2000 | 40 | 42 2500 | 50 | 52 3000 | 60 | 62 3500 | 70 | 72 4000 | 80 | 82 GRAPH LABELS: HUMBER WRAITH HUMBER WRAITH TITLE: ROAD WHEEL H.P. COMPARISON HUMBER SUPER SNIPE WRAITH 27 G VI 8 x 34 AXLE RATIO 6.50 x 17 TYRES NOTES: DYNO H.P. AT ROAD WHEELS BOTH CURVES CORRECTED TO 50°C AIR TEMP AND 45 lb/in² TYRE PRESSURE HUB HORSE POWER, I.E. DYNO H.P. + H.P. DUE TO ROLLING RESISTANCE OF REAR WHEELS N.B. A SMALLER DIFFERENCE IS APPARENT BETWEEN THE TWO CARS WHEN CONSIDERING HUB H.P. SINCE THIS MAKES SOME ALLOWANCE FOR WEIGHT. | ||