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. discussing test results on tyre cornering force and rim width.
Identifier | ExFiles\Box 157\2\ scan0048 | |
Date | 10th October 1936 | |
DUNLOP RUBBER CO.,LTD. TELEGRAPHIC ADDRESS: DUNLOPS PHONE, BIRMINGHAM. TELEPHONE: BIRMINGHAM CENTRAL 4108 (P.B.E.) EXTENSION No. 349 YOUR REF: HA/Gry.{Shadwell Grylls}9/MJ. OUR REF: LJL/T.286 FORT DUNLOP ERDINGTON BIRMINGHAM 10th Oct.1936 Messrs. Rolls Royce, Ltd., Experimental Dept. DERBY. For the attention of Mr G.H. Grylls. Dear Sir, Since our letter of the 14th August we have completed tests on the effect of rim width on cornering force. These tests have been carried out by our slow speed method on 6.00/16 6 ply E.L.P. covers but should be roughly applicable to other tyre sizes. Five rim widths have been used varying from 3.50 to 5.50. The attached tables and graphs show that there is no optimum rim width but that there is a progressive increase in cornering force with increase in the width of the rim. The order of increase is about 15% for a 2" increase in rim width, which is in line with the 5% increase obtained with the 6.00/18 tyres when the rim width was increased from 3.25" to 4.00". We have very little evidence as to what percentage increase of cornering force is noticable in actual service, but tests we have made at different pressures, at fairly high speeds on a car show that it is sometimes difficult to decide whether a reduced inflation can be detected. On the other hand a tyre which we made of special construction was found to wander and give a feeling of uncertainty in driving, and this tyre was much inferior to a normal tyre on our low speed cornering test. However you will be in a better position than ourselves to give a practical evaluation to percentage differences in cornering force. From the one curve you will also notice that a 2" increase of rim width is approximately equivalent to an increase in pressure from 20 to 30 lbs/sq.inch. The other curve shows that the relation between force and slip angle is approximately linear up to about 10° slip angle, but after this the force tends towards a constant value, the maximum pull being dependent on the coefficient of friction between tyre and the road. | ||