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).
Letter to the A.T. Speedometer Co. Ltd. detailing the results of tests on their speedometer instruments.
| Identifier | ExFiles\Box 50\4\ Scan181 | |
| Date | 17th March 1928 | |
| XL4308 c. EY. EP {G. Eric Platford - Chief Quality Engineer} + Mailing. EFCl/T. 17th March, 1928. Messrs. The A.T. Speedometer Co.Ltd., 20, Avonmore Road, West Kensington, W.14. Dear Sirs, We have made some tests of two of your A.T. speedometer instruments, Nos.B.140 N.488.14/52 and A.929.N.730.15/52, taken from recent supplies, the former with a K.P.H. scale and the latter with a M.P.H. scale. We were anxious to see exactly at what temperature these read correctly and what variation occurred between 18ºC and 30ºC. We are enclosing the results (exhibited in the form of a curve) of the tests of these two instruments, in which the conditions of test were very exact, particularly in the case of the speed at which the instrument was driven. Our most recently approved miles per hour and revs. per mile figures (derived from actual careful tests on the road) are in accordance with the following table for the 40/50 H.P. type instrument :- 40/50 H.P. Chassis fitted with 33" x 6.75" Balloon Tyres on 21" dia. rims. | Axle Ratio. | M.P.H. of car at 600 revs. per min. of speedometer. | Revs. per mile | |-------------|-------------------------------------------------------|----------------| | 14/52 | 45.0 | 800 | | 15/52 | 48.2 | 747 | | 16/52 | 51.4 | 700 | | 17/52 | 54.6 | 659 | Contd. | ||