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).
Summary of test results for Michelin Pilot tyres, comparing ride, handling, cornering power, and noise against standard tyres.
| Identifier | ExFiles\Box 158\1\ scan0184 | |
| Date | 11th May 1938 | |
| W/P. Sr. from Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} [Handwritten note] 1339: see 1245 for previous corrs. Rm{William Robotham - Chief Engineer}/FJH{Fred J. Hardy - Chief Dev. Engineer}7/R.11.5.38. MICHELIN PILOT TYRES. We have tested the Michelin Pilot tyres you sent to us, and the following is a summary of the results :- At the pressures which you told us to use, i.e. 20 lbs/square inch front, and 23½ lbs/square/inch rear, the Michelin tyres undoubtedly give a better ride and less general shake than either present standard 5.50 x 18 @ 30 lbs/square inch, or, future standard 6.50 x 17 @ 28/square inch. They also give less oversteer than either of our sizes but make the steering heavier. The chief drawbacks at the recommended pressures are that they have less cornering power than our large tyres, 0.49 sideways g against 0.54, and are very noisy. To obtain the same cornering power it is necessary to run the rear Michelins at 29 lbs/square inch, and the front @ 26 lbs/square inch. At these pressures both the ride and the steering chacteristics are identical to our 6.50 x 17 India tyres. This has been confirmed by skid pan and tyre deflection measurements. The only remaining advantage of the Michelin tyres is that a set of 5 tyres and wheels would weigh 115 lbs less than our 6.50 x 17, which is offset by the fact that they are far too noisy. We agree that they give better handling than the 5.50 x 18 India tyres, and we think that your impressions were probably the result of comparing the Michelin tyres with the small India tyres. We attach prints of curves showing the slip and oversteer angles of Michelin tyres at various pressures and the rating of the tyre at 1000 lbs load and various pressures. From the latter curve it will be seen that the Michelin tyre has the same rating as the India @ 28/lbs/square inch, namely, 1375 lbs in, when its pressure is 29 lbs/square inch. Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} | ||