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).
Analysis of variables like tyre size, inflation, and speed affecting A.T. speedometers.
| Identifier | WestWitteringFiles\U\August1930-November1930\ Scan037 | |
| Date | 4th September 1930 | |
| To R.{Sir Henry Royce} from EPC. c. Sg.{Arthur F. Sidgreaves - MD} c. WOR.{Arthur Wormald - General Works Manager} E.{Mr Elliott - Chief Engineer} c. Ds. Py. PN.{Mr Northey} ORIGINAL EPC2/AD4.9.30. X.4308. A.T. SPEEDOMETERS. In our EPC1/AD19.8.30 we mentioned the dependence of road wheel and speedometer drive revolutions per mile upon :- (1) Tyre size (2) Degree of inflation (3) Speed. Actual variations which have been noted are as follows :- (1) In the case of Phantom II it is understood that the standard tyres at normal inflation pressure and slow or moderate speed give 609 wheel revolutions per mile, whereas the largest tyres in use give, in similar circumstances, 595 revolutions per mile, a reduction of 2.3% (2) Tests which have been made have shown that the road wheel revolutions per mile of Dunlop Silent Tread tyres on both chassis are increased by nearly exactly 3% by a reduction in tyre pressure from 40 to 20 lbs/sq.in. This result is presumably at slow or moderate speeds. At high speeds the effect would probably be less. (3) As mentioned in our report EPC1/AD19.8.30, tests appear to have shown that the road wheel revolutions per mile are decreased by 2½% at very high speeds as | ||