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).
Specification document for the speedometer drive on the Wraith II gearbox.
| Identifier | ExFiles\Box 165\4\ img383 | |
| Date | 23th November 1936 | |
| 6065 c/ Dr.Ex. Ey/ED.{J. L. Edwards} RM{William Robotham - Chief Engineer}/WSt. E/HDY.{William Hardy}1/HP.23.11.36. Wraith II Gearbox. Speedometer Drive. The speedometer for the first Wraith II car or two, with 25/30 back axle centre casing and gears should be made to suit the following particulars:- Axle ratio - 9/41. Servo drive ratio -2/21. Speedometer gear ratio 21/8. Rolling radius of tyres 14.850". at 30 m.p.h. Feet per rev. 7.780. Speedometer revs per mile. 5280 X 41 X 2 X 21 / 7.780 X 9 X 21 X 8 = 772. The tyre rad. given assumes 17" x 7" tyres on either 5" rims to GW.449 or 4" rims to GW.429. We understand that Messrs. India Tyres have quoted to Ey/Mtn a rolling radius in connection with GW.449. Messrs. Dunlop give 14.850" for their 17" x 7" tyres and 4" rim. E/HDY.{William Hardy} | ||