Most three arm alloy cranks use a 116 BCD pattern, which is actually a ca rryover from the circle used by many older cottered steel three arm cranks including Stronglight. Stronglight, Nervar and TA, among others, made th ree arm 116 BCD alloy cranks in addition to the three arm Campy GS. I kn ow chainrings are largely interchangeable among the other brands, and I thi nk these should interchange with Campy GS as well. I seem to recall that least some of the Campy GS three arm cranks had the inner ring riveted to the outer, which I find annoying in terms of limiting ring choice, although one could probably cut the rivets fairly easily. The three arm cranks d o generally use different diameter (smaller I think) chainring bolts than 5 arm cranks, but I believe that size is the same for all major brands.
There are a fair number of Stronglight rings still around with a 116 BCD si x hole pattern. These originally puzzled me, but I'm now 99% sure that t hey were made not for some 6 arm cranks, but for the three-arm 116 BCD cran ks. The second set of holes is for attaching the inner ring to the outer ring. Another clue that this was the case is that one also sees some 11 6 BCD inner three-hole rings with the webbing partly cut away at the three points midway between adjacent bolt holes. This was evidently done to al low the inner ring web to clear the bolts used to attach the six hole outer ring to the arm. On the old steel cottered cranks, these bolts were not recessed, and threaded into threaded holes in the crankarms from the bac kside. I'm not sure that the bolt heads would have protruded far enoug h to push against the inner ring web, but cutting away the webbing gave eas ier access to the bolts to allow both rings to be attached or removed f rom the cranks without separating the rings from each other. All of this ma kes me believe that both 6 hole and 3 hole 116 BCD alloy rings were origina lly introduced to allow the use of lighter weight rings with a wider gear r ange on the old three arm steel cottered cranks which earlier were typica lly seen with "carrier" brackets to which the rings, often steel ones, at tached at a much larger BCD. Dispensing with the carriers and attaching an alloy outer ring directly to the crankarm with an inner attached to the outer allowed a much larger range of gearing on these crankarms.
I think the alloy three arm crankarms developed later than the rings, per haps initially using the 6 hole outer, but more recently using three hole i nner and outer both attached to the arms with a single set of bolts a s seen on the three arm TA Professional found on early 70's Raleigh Compe titions.
This would be replaced by the three arm Campy GS on the mid 70's Raleigh Co mpetition GS, and I think the late 70's Competition GS shifted to the 5 arm 144 BCD Campy GS, which was basically a less highly finished NR. I believe the last version of the Campy GS was the one that stayed with 5 arms, but returned to the 116 BCD circle used earlier on the three arm G S. The old 116 BCD circle allowed use of a smaller inner ring, which was particularly useful as this last GS was typically configured as a triple, with all three rings attached with one set of triple chainring bolts in the manner of Stronglight model 99 triples. The 5 hole 116 BCD rings on the last Campy GS were also used on the Campy Victory and Triomphe at the start of the Off Topic period which began with introduction of C-Record. It used to puzzle me where Campy came up with the 116 BCD circle on Victor y/Triomphe, but it appears it originated with the old cottered steel t hree arm cranks decades earlier.
Regards,
Jerry Moos
Big Spring, Texas, USA
From: Stronglight49@aol.com <Stronglight49@aol.com> Subject: Re: [CR] GS Chainrings To: classicrendezvous@bikelist.org, beandk@rcn.com Date: Friday, November 14, 2008, 10:46 AM
As Joe mentioned, one of the oldest patterns. 116 mm BCD Here is a quick scan I just uploaded. Handy info... from Sutherlands, 1st ed. 1974.
http://farm4.static.flickr.com/
BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA
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