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).
The results of testing Michelin 425 x 40 tyres, detailing performance and future requirements.
| Identifier | ExFiles\Box 146\5\ scan0032 | |
| Date | 29th October 1938 | |
| W/F.{Mr Friese} To Sr. from Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} c. By.{R.W. Bailey - Chief Engineer} c. Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} MICHELIN TYRES. We have now completed our tests on the Michelin 425 x 40 tyres and attach two prints of a graph showing the results. As can be seen the Michelin tyres have a very small slip angle and are very good in this respect. A test on the road confirmed this and also showed that they gave good directional stability and freedom from wandering. The tyres are, however, too noisy at all speeds when travelling straight or during mild cornering. They are commendably free from squeal during hard cornering. The ultimate maximum cornering power of the tyres was the same as that of the India tyres. Our experience is that it is essential to have continuous shoulders to the tread to obtain silence and we suggest that Michelins should incorporate this on any further tyres they make for us. We wish to be able to fit these tyres to B.III cars with pressed steel wheels, and if Michelins can supply us with 5 rims we will have them built on to pressed centres by Dunlops. Will you please obtain for us if possible, 5 rims without spoke holes. We would also like a drawing of the rim and of the profile of the tyre cross section so that we can arrange the various clearances etc. Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} | ||