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).
Report analyzing horsepower losses and comparing maximum lap speeds with various tyre types.
| Identifier | ExFiles\Box 158\2\ scan0019 | |
| Date | 17th May 1939 | |
| -5- RM{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}15/JH.17.5.39. Although the clutch H.P. appears to top the hub horse power by some 6 H.P. at the peak, it should be remembered that this curve has been obtained from a similar engine on the test bed and that the silencer losses have only been approximated to, therefore, the engine in the car may easily give two or three less horse power at the peak, leaving a more reasonable difference for gearbox and transmission loss. Brooklands tests with 7.B.V. Comparison of max. lap speeds with various tyres. A constant hub horse power of 100 has been assumed over the speed range obtained, and from this is deducted the horse power required for windage, based on a frontal area of 24 sq.ft. and a K of .0017. The horse power remaining is required to overcome the losses in the four wheels, and this is compared with the losses which would have been obtained on the dyno. A glance at these figures shows that the most important thing now is to devise means of measuring road wheel loss on the road. Type of Tyre and lap speed. | H.P. due to windage. | H.P. remaining for tyres. | Tyre loss from dyno. figures. m.p.h. Michelin. | 88 | 74 | 26 | 25 Dunlop racing | 90.06 | 79.5 | 20.5 | 13.5 India. | 86.6 | 70.6 | 29.4 | 42. India. (Initial run) | 85.13 | 67.2 | 32.8 | 47. Avon. | 88.38 | 75 | 25 | 33.5 Avon. (Initial run) | 85.28 | 67.4 | 32.6 | 33.5 | ||