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).
Explaining the effect of wind on the maximum speeds of touring cars.
| Identifier | ExFiles\Box 178\1\ img013 | |
| Date | 15th February 1926 | |
| Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/LG15.2.26. FUNDAMENTALS OF CAR PERFORMANCE. Effect of wind on the maximum speeds of touring cars. The maximum speeds on the level in still air of the two R-R touring models are 61 and 72 m.p.h. respectively. We frequently hear of speeds considerably in excess of these figures being attained by cars in customers hands. We ourselves have recorded over 70 m.p.h. on the 20 HP., and over 80 m.p.h. on the Phantom with favourable winds. This may seem somewhat surprising in view of the fact that directly favourable or contrary winds exceeding 10 m.p.h. are a very exceptional occurrence on the road. The explanation is that wind resistance absorbs over 75% of the total HP. available at the maximum speed of the car. Wind resistance is also proportional to the square of the speed. Therefore if the air speed of the car is dropped 10 m.p.h. due to a following wind, the H.P. required to drive it is lowered very appreciably and the maximum road speed increased accordingly. This is set out in the attached graph 1. The H.P. to drive the car at 70 m.p.h. with a following wind of 20 m.p.h. is:- H.P. to overcome rolling resistance 70 m.p.h. H.P. to overcome wind resistance of 50 m.p.h. An interesting point to notice is that a normal touring car does not gain as much in speed from a following wind as it might, owing to the fact that it is under geared to obtain good contd. | ||