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 to Dunlop Rubber Co. Ltd. detailing tyre pressure tests and their effect on wear and mileage for cord tyres versus fabric tyres on a 40/50 HP chassis.
| Identifier | ExFiles\Box 39\2\ Scan094 | |
| Date | 29th September 1921 | |
| C O P Y. hsl/LG. 29th. Sept. 1291. Messrs. The Dunlop Rubber Co.Ltd., Aston Cross, Birmingham Dear Sirs, For the attention of Mr. Paull. Sometime ago we wrote to you with reference to cord tyres and tyre pressures. We have since carried out further tests with still lower tyre pressures. On a 40/50 H.P. chassis fitted with an open-touring body weighing 42 cwts. we have obtained the following record with tyres:- With the rear tyres pumped to 80 lbs. pressure we wore through the tread until the fabric was just showing after 3,150 miles and 3,275 miles. With the tyre pressures at 65 lbs. the tread was worn through after 4,050 miles and 4,275 miles. We are now running with the tyres pumped to 45 lbs. pressure - they have run so far, 3000 miles. We are certain, from the appearance of them, that they will make a better mileage than any of the others. As you are no doubt aware, the difference in the riding of the car with tyres pumped to 70 and 80 lbs. compared with tyres pumped to 40 and 50 lbs., is tremendous. There is also a big difference in the wear and tear on the chassis, it being of course, considerably less with a lower pressure. We feel that a user does not get value out of the tyre if it is run with high pressures and he is bumped over the road and after that the tyre is thrown away because the tread is worn through. In a conversation we had with you, we remember you stating that a cord tyre gave a better balanced tyre as regards wear, meaning, that the tread and the casing would have a similar life. We think that this is right if the correct tyre pressure is used and we believe that the tyre pressure could be considerably lower with the cord tyre than we have been using on the fabric tyre. We wish to circulate to R-R Owners, that when using cord tyres they can run with a lower tyre pressure than with the fabric tyres. The pressure we have in mind are:- 1. For light open-touring car up to 42 cwts. 45 to 50 lbs. 2. Heavy touring cars up to 50 cwts. 55 to 60 lbs. 3. Cars over 50 cwts. 60 to 65 lbs. We should be greatly obliged if you would let us have your views on this matter. Contd:- K.R.&S. (100) 1M. 18-11-20. (SLO) T.S. 28/2 B | ||