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).
Wheel revolutions per mile for Phantom A.T. speedometers under various tyre conditions.
| Identifier | ExFiles\Box 59\2\ Scan109 | |
| Date | 3rd March 1931 | |
| Hs{Lord Ernest Hives - Chair}/AJL. from EFC. c. Hs.{Lord Ernest Hives - Chair} X605/a EFC1/AM.3.3.31. X.6051a PHANTOM A.T. SPEEDOMETERS. Our most up-to-date information on the above as recorded in our report EFC2/AD4.9.30 is (1) Wheels fitted with standard tyres at normal inflation pressure of 40 lbs/sq.in. make at slow or moderate speeds 609 wheel revolutions per mile. The largest tyres in use make, in similar circumstances, 595 revolutions per mile. (2) The wheel revolutions per mile with Dunlop silent tread tyres are increased 3% by a reduction in tyre pressure from 40 to 20 lbs/sq.in. this result being at slow or moderate speeds. (3) At normal inflation pressure, the road wheel revolutions per mile are decreased by 2½% at very high speeds as compared with those at slow or moderate speeds. We have put on order two Veeder counters which will be handed to you on receipt for the purpose, as arranged in conversation with you as a result of PN{Mr Northey}'s note PN{Mr Northey}4/WTLO.3.31, of checking as far as is conveniently possible the above figures. In the meanwhile, however, we should like you to say if you agree sufficiently well with the above figures to enable us to proceed to obtain an experimental A.T. speedometer with the quantities based on these figures including the very desirable artificial contraction of the scale at the high speed readings. EFC. | ||