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).
Tyre performance, including rim widths, ply limits, inflation standards, and the introduction of Rayon fabric.
| Identifier | ExFiles\Box 170\3\ img175 | |
| Date | 7th December 1938 | |
| -2- Mr. S.W. Grylls. 7th December 1938. It is also based on the normal rim widths specified in the table on page 10 of the Tyre & Rim Year Book. (Increase in rim width increases tyre section about half as much and therefore increases carrying capacity). It is found by test that the cornering power of all 16" tyres inflated to Tyre & Rim standards and on normal rims is between ten and eleven percent of the load carried per degree of slip angle. (Tested on steel drums). Therefore, all other things being equal, a car which has Tyre & Rim inflations for the loads carried front and rear, will neither over nor understeer. American practice is now to inflate to Tyre & Rim standards. You will notice that the four and six ply limits are clearly marked on the Tyre & Rim chart, but no difference in loading is allowed. At first sight this does not seem reasonable, since the six ply tyres are certainly stiffer vertically and therefore require higher loads for the 13% deflection standard. I have not discussed this with the tyre men, but imagine it is because there is relatively more danger of tread separation and sidewall breakage in the 6-ply. I think it is true to say that all American cars except, perhaps, the big 90 Cadillac and the Packard 12, are turned out with 4 ply tyres, and in several cases the loading and the corresponding inflation of the rear tyres is above the 4 ply limit. You will find no trouble with bursting on 4 plys if properly made and inflated. The cure for bursting in tyres which are driven hard for long mileage is undoubtedly the use of Rayon fabric, introduced by Goodyear last year. The tensile strength of Rayon fabric drops about 15% at 275°F.{Mr Friese} | ||