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).
Wraith car performance in France, axle ratios, weight, and future design alternatives.
| Identifier | ExFiles\Box 108\1\ scan0414 | |
| Date | 24th February 1938 | |
| Sg.{Arthur F. Sidgreaves - MD} from Rm.{William Robotham - Chief Engineer} Hs.{Lord Ernest Hives - Chair} c. By.{R.W. Bailey - Chief Engineer} 600a Rm{William Robotham - Chief Engineer}1/R.24.2.38. WRAITH CAR IN FRANCE. We have been talking on the telephone to Waller at Chateauroux, and he states that now that his engine has freed up he is running into the main torsional period of the crankshaft on top gear when the small wheels are fitted to the car. This is, of course, an impossible situation as it would soon result in a broken crankshaft. We have therefore told him to confine future running to the larger wheels which are equivalent to the 7.7% higher axle ratio(large wheels have been sent out). In view of the fact that all Wraith cars are likely to go on the Continent, the low axle ratio does not seem to be a practical proposition. Regarding the performance of Wraith cars generally, the weight of experimental cars has come out very similar to that of the 25/30. Generally speaking, however, experimental cars are lighter than the corresponding production cars, and the Wraith will be no exception, as we are substituting cast iron drums for light alloy drums. Additionally, however, we should like it to be remembered that we have 6" more room between the windscreen and the rear axle for body space. On experimental cars we have not made use of this 6" to increase the size of body, but rather to enable the customers to sit further forward of the back axle, and so get an improved ride. We understand, however, that bodies in hand for Wraith cars now will have increased room, and even if this is not done officially Coachbuilders will certainly take advantage of the increased space provided. The net result of this is likely to be that the curb weight of complete Wraith cars may approach 43 cwts. There is no doubt that under these conditions the Wraith performance must be worse than the present 25/30, even with the same axle ratio, and we fully appreciate this fact in asking for the higher top gear. If lack of direct drive performance is likely to be a serious sales resistance on this type of car, there appear to be two alternatives, an overdrive box or a larger engine. The first might be available in twelve months, the second in three years. Rm.{William Robotham - Chief Engineer} | ||