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).
A.T. Speedometer data sheet with calculations for Phantom II and 20 HP models.
| Identifier | ExFiles\Box 59\2\ Scan009 | |
| Date | 3rd February 1930 | |
| X.4308 3.2.30. A.T. SPEEDOMETER DATA. The following are the quantities which come under consideration :- (1) Road wheel revolutions per mile. For various Phantom II tyres these are :- Standard 608.7 Minimum 595 20 HP Standard 660 (2) Gear ratio of road wheel to speedometer drive :- Phantom II standard 41/11 x 2/18 x 26/8 = 1.346 20 HP. " 50/11 x 2/16 x 20/10 = 1.136 (3) ( = (1) x (2) ) Speedometer drive revolutions per mile. Phantom II standard 819 " minimum 801 20 HP. standard 750 (4) Speedometer instrument spindle revolutions per indicated counter mile. It is possible for the makers, in the design of the internal gearing, to provide instruments with certain figures only for this quantity e.g. 800, 765, 740. In any particular case they should be provided with our minimum possibility for (3) (and not with any (1) or (2) data at all) and asked to provide an instrument with a (4) figure which is the one nearest to our (3) figure on the lesser side e.g. for Phantom 801 say 800. for 20 HP. 750 say 740. N.B. Present standard Phantom II speedometers are 765 revolutions per mile and give mileages | ||