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. about power losses in tyres and vehicle testing results.
| Identifier | ExFiles\Box 157\1\ scan0091 | |
| Date | 8th July 1933 | |
| Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/KT. July 8th 1933. Mr.Healey, The Dunlop Rubber Co. Ltd, Fort Dunlop, Erdington. B'ham. Dear Healey, You will remember some time ago I asked you whether you had any information as to the power losses in tyres transmitting power, and you replied in the negative. I wonder whether you are in a position to give us any figures on this subject at the present time. The matter is of renewed interest today because we are carrying out experiments on the windage of our cars, and to compute the drag of a vehicle accurately we need to know the correct H.P. delivered by the road wheels. The information we have at present indicates that running on a curved drum, the tractive resistance of one of your tyres is between 35 and 45 lbs/ton. Your ref. AGP/HR. of 4.1.32. Taking the intermediate figure of 40 lbs/ton, on a car we have been testing, the rear axle weight being about 18 cwt., we find that the H.P. absorbed by the tyres on the back axle at 85 M.P.H. is approx. 7½. The actual difference between the measured clutch H.P. and the measured drum H.P. is not less than 22. There is therefore a discrepancy of 14½ HP. between the two figures. We are certain that no more than 5 HP. would be lost in our gearbox and axle in transmission inefficiencies and oil churning losses, and are therefore left with 10 H.P. which we are unable to account for except as inefficiency in power transmission of the tyres. The actual tyres we are using are of 5¼" section on 18" rims, and the tests were carried out on the Bentley. We think that these results are of direct interest to tyre manufacturers, as the rear tyres appear cont'd | ||