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).
Rear axle ratios and their effect on the performance of the 'New Phantom' car.
Identifier | ExFiles\Box 66\4\ scan0323 | |
Date | 28th July 1925 | |
(6350) To Hs.{Lord Ernest Hives - Chair} from BJ. BJ3/H28.7.25. REAR AXLE RATIOS. The following is an extract from PN{Mr Northey}5/DN14.7.25, for your information and consideration. "We must be careful, however, to realise that there are various factors which may have to be taken into account in fixing these ratios. In the case of an open car designed with a view to achieving high speeds when desired, the gear ratio should be of such a value that the highest speed which the complete car is capable of giving on the level should be limited only by the critical point having been reached when the valves tend to leave the tappets. In the case of our open trials 'New PhantomCodename for PHANTOM I' although the performance of this car is quite good in most respects, including acceleration, it is, I believe, when running under favourable conditions on the level, not capable of achieving a high speed than 74 or 75 m.p.h. Meanwhile, the valves would not tend to leave the tappets with this car (15-tooth axle) until a road speed of about 83 m.p.h. had been reached, a condition which it will apparently never achieve, obviously if a higher gear ratio (i.e. 16-tooth axle) were placed on this car, we should be merely at a further disadvantage in respect of speed as well as acceleration, in view of what I understand to be the shape of the power-curve of the engine up to 2700 revs." Since this was written, I understand the car has done 79 m.p.h., and we have arranged to continue to use it in its present state. B.J. | ||