Steering and tyre performance tests on various models, including pivot lean and steering tube load analysis.
| Identifier | ExFiles\Box 11\2\ 02-page274 | |
| Date | 14th July 1929 | |
| 121 To Hs. {Lord Ernest Hives - Chair} From Rm. {William Robotham - Chief Engineer} Hôtel de France Châteauroux France. 14/7/29. Re: 21-EX STEERING.- We have to-day tried the 7" tyres on 20" rims, various pivot leans, and various side steering tube settings on the S.S. front axle; The standard front tyre pressure we test at is 35 lbs. per sq. in. 7" tyres on 20" rims.- You will remember that the history of these tyres is that they superseded 6.75" tyres on 20" rims which were originally fitted to 18-EX and turned down as being hopeless for steering. We had not run these 7" tyres very much at Derby, but were under the impression that they showed an improvement. The conditions for testing steering being so much better out here, we can now say that these tyres are 20% worse for joggles than the standard S.S. tyres on 21" rims, 10% worse for selectiveness, and give 20% heavier steering for parking. We think that we should therefore avoid fitting 20" rims to the S.S. until we have successfully got some cars into production and got owners' views of the steering. We have not run into any high speed wobbles with these tyres and they should not by any means be considered as being hopeless, but they are not as good as those we have at present. The main difference between the tread of these 7" tyres and the 6.75" tyres is that they are about 1/2" wider and the non skid grooves about 1/3 m {Mr Moon / Mr Moore} /m deeper. Pivot lean.- We think that the best compromise at which to start off the S.S. is 3°, as is always the case, better results for certain conditions can be obtained by having more or less than this lean. Shunting.- We think that the present type side steering tube M. {Mr Moon / Mr Moore} Sch. 2301 is much more adaptable than the one we previously had, and therefore it will be possible to cater for the individual requirements of customers. We have not yet completed our tests, but the Works will be able to reproduce our results when the cars are on test without the necessity of new parts. It would appear that the best setting for the conditions under which the majority of R.R. cars are used, would be somewhere between the figure given by G.W.H. and the present production setting. Cross steering tube load.- We have been doing all our tests on the S.S. axle with a cross steering tube load which gives 60 lbs. measured at the ball end of the side steering tube steering arm. We find that the load on 12-EX axle is 35 lbs. We are therefore increasing this to 60 lbs. and refitting 12-EX axle so that we shall get an exact comparison, as up to date | ||
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).