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 concerning the breakage of wire wheel spokes, comparing American-made with Dunlop spokes, and detailing material tests.
| Identifier | ExFiles\Box 159\1\ scan0103 | |
| Date | 28th July 1925 | |
| 1b Oy6-W-72825 July 28, 1925. Mr. Claude Johnson, Rolls-Royce, Limited, London, England. (Copy for attention of Mr. Royce Mr. Platford Mr. Hives Dear Sir: Re Wire Wheel Spokes We have recently received uncompleted standardisation sheet for straight spokes in Dunlop wheels, to cure breakage of spokes. We can only recall three or, at most, four cases of spokes breaking in legitimate use on post war Dunlop wheels. We have had no case of spoke breakage on the American-built Dunlop type wheel which we are now using. Even in 20,000 miles very strenuous use on test no spoke breakage occurred. The wire used by the American makers is .205 swaged to .175 diameter. We believe the Dunlop spoke is about .008 smaller, namely, .167 diameter. The steel used by the American makers is as follows-- Carbon .50% Manganese .70% Silicon .20 Phosphorus .05 max. Sulphur .03 " The spokes must stand from 5 to 7 180º cold bends. Actual tests give-- Yield point Ultimate R.A. Elong 2" Elong 4" Remarks No. 1 American 135,000 161,000 45% 5% 5% 1/2 Cup No. 2 " 140,000 151,000 49.5 7.5 7.5 Full cup No. 3 Dunlop 160,000 171,500 45 (Broke outside Full cup gage marks) No. 4 " 155,000 166,500 42 5 2.5 1/2 cup | ||