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).
Analysis of power losses related to different tyre types, tyre sizes, and performance in various gears.
| Identifier | ExFiles\Box 158\2\ scan0041 | |
| Date | 9th June 1939 | |
| -3- Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}5/JH.9.6.39. In the case of India tyres the losses increased slightly with the increase in tyre size. Thus there is about 1% more loss between 70 and 90 m.p.g. with the 18" tyre than with the 16", and the 17" lies somewhere between these two. There is a much greater difference between the two types of racing tyre tested. In the previous memo. on tyre loss the 16" racing tyre was the only one which apparently did not lose 1.5 times more power on the drums than on the track. According to the comparative curves on sheet 9, this 16" tyre loses about 65% less power than the 19" tyre. Had it only lost 20% less, and so come into line with the India curves on Sheet 8, it would have been just about 1.5 times worse on the drums than on the track. (4) Losses at full throttle in each gear (Curve sheet 10,11). Full throttle curves in each gear were obtained with Dunlop tyres. Since the 1st. gear curve was obviously influenced by deformation due to torque, curves of the rear axle torque in each gear were drawn. It will be seen that in 1st. gear the loss is almost exactly proportional to the torque transmitted. 2nd. gear and direct gear curves are also distorted. This is particularly impressive in the case of direct gear where the hump due to torque is apparent at middle speeds, and the rapid rise at high speeds is found as in the overdrive curves. It should be pointed out that whereas overdrive curves have frequently to be repeated to make quite sure that some point should really not be there, direct, 2nd, and 1st. gear curves have been found to be remarkably steady, repeatable hour by hour and day by day. Similar tests were made with India 6.50 x 16 tyres except in 1st. gear. In this gear the wheels spun and the test had to be abandoned. The 2nd. gear test gave results almost exactly similar to the Dunlop 2nd. gear test, except that there was no increase in loss at 15 m.p.h. In direct gear however the curve showed no appreciable hump at middle speeds and followed very closely the overdrive curve. It seems probable therefore that these differing torque effects occur as the result of deformations arising from differing tyre constructions. Similarly, the higher the tyre pressure, the less the deformation, and the more similar direct gear losses | ||