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).
Tyre performance and power losses, comparing Andreau's formula with dynamometer and road test results.
| Identifier | ExFiles\Box 158\2\ scan0018 | |
| Date | 17th May 1939 | |
| -4- (5) Andreau's formula - see curve sheets 2, & 6. It will be seen that the power loss on the dyno. derived from this formula is not too bad so long as old tyres at high pressure are used. If however, new tyres are run at their normal pressure it appears to be very conservative. It is being compared with dyno. losses however, and it may well compare better with actual road losses. Excessive losses with new India tyres. With the exception of India tyres, every other type rose up off the drum due to centrifugal force as the speed increased. Exactly the opposite was the case with the India, and at normal pressures at about 90 m.p.h. a standing wave became apparent behind the point of take off from the drum. This is illustrated in the accompanying photograph. The wave increased in amplitude with speed and reduction in tyre pressure. With tyres at 46 lb/in.sq. the wave had not appeared at 100 m.p.h. With tyres at 22 lb/in.sq. the wave commenced at about 75 m.p.h. A tyre with tread worn off was then tried, but nothing unusual happened up to 100 m.p.h. with normal pressure. When the pressure of this tyre was dropped to 22 lbs. the wave just became apparent at 100 m.p.h. Very erratic losses were recorded at high speeds with new India tyres, and these losses were always in excess of those obtained with other tyres, especially at low pressure. T.E.V. Power Curves. The accompanying curves serve to show that the tyre losses obtained by the above method can be applied to dyno. curves obtained at different road wheel speeds to give resultant hub horse powers almost identical and accurate within a small margin of error. | ||