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).
Letter from the Avon India Rubber Company discussing tyre performance, comparing five-bar and four-bar designs.
| Identifier | ExFiles\Box 156\3\ scan0272 | |
| Date | 5th December 1941 guessed | |
| AVON INDIA RUBBER CO. LTD. It is our opinion that if the original five-bar tyres which you tested so extensively in the early part of 1939 were as liable to squeal as our present Standard Silent Tyres, your tests would certainly have brought this fact to light. This points strongly to the factors tending to produce squeal having crept into the design during the subsequent change to the four-bar design, or in the still later modifications made in the summer of 1939 to render the four-bar design less liable to uneven wear. When these changes are examined in detail it is evident that several of the dimensional alterations might have contributed towards this tendency to squeal. Moreover, when the present Standard Silent pattern and our Special Speed pattern are examined under the pressure glass there is a wide difference in behaviour. In the Standard Silent Tyre there are zones of extreme movement and zones of distinct rigidity, whereas with the Special Speed tyre there is generally more flexibility and the flexibility is evenly distributed over the foot print. In the light of these facts therefore, we have decided that it would be prudent to revert to the original five-bar design as the basis of future experiments and we have therefore ordered a casting for a 6.50/16 mould. Delivery of this casting has been promised in about 10 weeks time from now, by which time we hope to have made up our mind on detailed dimensions. The finished mould should be available in about 16 weeks time from now. Yours faithfully, THE AVON INDIA RUBBER COMPANY LIMITED. J.{Mr Johnson W.M.} G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Mackay DEVELOPMENT MANAGER AND CHIEF CHEMIST. [Handwritten Note] Tests with above tyres on Milford Bridge Show no appreciable difference in noise All tyres being noisy at a speed as low as 15-16 MPH. | ||