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).
Recommendation to alter A.T. speedometer internal gearing to improve accuracy due to temperature and tyre pressure issues.
| Identifier | ExFiles\Box 59\2\ Scan006 | |
| Date | 30th January 1930 | |
| X4308 [REDACTED]Y. From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to EFC. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} a/MJ.30.1.30. A.T. SPEEDOMETERS. We find that the average running temperature of the A.T. speedometers appears to be higher than we have allowed for, especially in closed cars which at present form the bulk of our production. The result is that on the road the M.P.H. reading can actually be low compared with the trip reading (which is the reverse of what we consider desirable.) We also find that with the very low tyre pressures which customers insist on using, the mileage recorder is inclined to be too optimistic. We therefore recommend that the speedometer internal gearing on the S.S. and 20 HP. should be altered by increasing the revs/mile by as nearly as possible 5%. i.e. 800 revs/mile Phantom ll and 735 revs/mile for the 20 HP. while the M.P.H. reading should be set at 35°C for this gear ratio but with a minimum + 3% above this figure to allow for the higher temperatures which we know are frequently attained. This will give us a 5% reduction in mileage measurement and maximum 2% reduction in M.P.H. recording which should be more satisfactory than the present arrangement. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||