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 Dunlop Rubber Co. Ltd. detailing the results and methodology of tyre rolling resistance tests.
| Identifier | ExFiles\Box 53\2\ Scan255 | |
| Date | 1st October 1926 guessed | |
| page two. The distance rolled on 33 x 5 tyres at 45 lbs/sq.in. was 1096 yards, and on 33 x 6.75 tyres at 30 lbs/sq.in. 1088 yards. The ratio between the two is much smaller than in the case of the machine test for several reasons:- 1. In the machine test the tyre runs on a circular drum, the deflection under a given load being greater than if the tyre were resting on a flat surface. The 33 x 6.75 tyre, having a longer contact, is relatively more affected by this than is the 33 x 5 tyre. 2. In the machine test practically all the resistance measured is caused by the tyres, whereas in the road test the rolling resistance of the tyres is only one factor in the total rolling resistance of the car, the other factors remaining approximately constant when the tyres are changed. 3. The machine test is carried out at a constant speed of 50 m.p.h. while in the road test the speed varies gradually from zero to a maximum of about 40 m.p.h. and back again to zero. We trust that these tests will provide you with the information you require. Yours faithfully, [Signature: A Healey] for the DUNLOP RUBBER CO. LTD. Total car T.R. at 50 M.P.H. = 85 lbs/ton Increase in T.R. due to Balloon Tyres = 15 lbs/ton | ||