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An old twist
Highwheelers used steel cranks, not aluminum.
A clever fellow figured out that he could twist round steel cranks to make them stiffer. Late-era highwheeler racers liked the twisted cranks because the pedals didn't give as much, even though the cranks weighed only about half as much: "Known as 'Southard's Twisted Cranks,' they were an invention of a Southampton man of that name, under his patent No. 17408/1889, and embody an extremely clever principle. Each crank was forcibly twisted exactly half a turn--when cold--the claim being that, after this treatment, the metal would not twist any more on violent pedal pressure being applied to it. Obviously left and right cranks were were twisted in different directions and were not interchangeable. Southard's cranks were stated to weigh only 7 ounces [~200 grams] the pair, against 16 ounces [~455 grams], the alleged weight of the standard cranks of the period. For some time after their introduction they enjoyed considerable popularity." --"Bartleet's Bicycle Book," p. 52 The upper highwheeler is the late-model Humber racer (a radial re-spoked to tangent, which Humber despised) with the weight-weenie Southard cranks: http://i31.tinypic.com/8ysvuq.jpg Thin Southard crank detail: http://i25.tinypic.com/11aecyc.jpg Hideously overweight ordinary crank: http://i32.tinypic.com/vcudcl.jpg The Southard cranks are noticeably thinner than the cranks on the lower highwheeler. (Yes, those are toe-clips on the Humber with the thin Southard crank. Naturally, both racers lack mounting steps.) "Fig. 26 is an illustration of 'Southard's' patent crank fitted by the same cotter pin. This is truly a beautiful crank; its specialty consists in the mode of manufacture. They are made from soft steel, a bar of which is twisted _cold_ , after the fashion of a coil of rope; when a certain stage is reached, the steel offers enormous resistance to being further twisted in that direction. The cranks are supplied in left and right, and, although they weight just half the weight of old crank, the utmost strain a rider can put on them will never bend or break one." --"English Mechanic," 1893, p. 445 http://books.google.com/books?id=DIU...page#PPA445,M1 Here are the cranks, the thin Southard being second from the bottom: http://i27.tinypic.com/2it361z.jpg Sharp mentioned the Southard crank: "122. Raising of the Elastic Limit.—Let a bar be subjected to a stress—represented by the point k (fig. 111)—considerably above its elastic limit. If the load be removed and the bar be again tested, it will be found that it is elastic up to a stress as high as that indicated by k. Thus the elastic limit in tension of a material like mild steel can be raised by simply applying an initial stress a little above the limit required." "An important application of this principle occurs in the case of Southard's twisted cranks. Here the cranks are given a considerable initial twist in the direction in which they are strained while driving ahead ; their strength is considerably increased thereby. A twist (sec. 109) is equivalent to a direct pull along certain fibres, and a direct compression along other fibres at right angles. The initial twist in Southard's crank is, therefore, equivalent to raising the elastic limit of tension of the fibres under tensile stress, and the elastic limit of compression of the fibres under compressive stress." --"Bicycles & Tricycles," 1896, p. 138-9 http://books.google.com/books?id=gFM...page#PPA139,M1 Sharp points out that the twisted crank is weak under back-pedal pressure, emphasizing why the cranks came in left and right and were for racers: "These considerations, when applied to the case of Southard's cranks, detract from the value of the initial twist. The line t t (fig. 109), which is the tension line when the rider is pedalling ahead, has had its elastic limit in tension artificially raised, and its elastic limit in compression artificially lowered by the initial twist. When back-pedalling, t t becomes the compression line. A twisted crank is therefore weaker for back.pedalling than an untwisted crank of the same material." --"Bicycles & Tricycles," 1896, p. 140 http://books.google.com/books?id=gFM...page#PPA140,M1 Cheers, Carl Fogel |
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#2
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An old twist
Interesting post Carl...and yet, you failed to mention that there are
more than a few twisted cranks in this newsgroup. Imagine that.... ABS |
#3
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An old twist
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