[CR]6-hole chainrings and alloy rings for those old cottered steel cranks

(Example: Racing:Jacques Boyer)

Date: Thu, 2 Aug 2007 12:22:03 -0700 (PDT)
From: Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net>
To: classicrendezvous@bikelist.org
In-Reply-To: <BAY142-F39D194936FAADAB50B5F0685E90@phx.gbl>
Subject: [CR]6-hole chainrings and alloy rings for those old cottered steel cranks

In my investigation of 3-hole chainrings spurred by changing the ratios on my newly rebuilt 1974 Raleigh Competition with TA Professional, I've come across Stronglight 6-hole 116 BCD alloy rings. These can be used on 3-arm cranks simply by using half the holes. But one then wonders what the extra 3 holes were for. I think TA did make an adapter with a 116 BCD 6-hole bolt circle, but as I've never actually seen one, I have trouble believing all the 6-hole 116 BCD rings out there, which do show up fairly frequently, were for a fairly obscure TA adapter.

I therefore have another theory. As many know, the old steel cottered cranks had both rings attached inboard of the arms. Typically a fairly short bolt would thread directly into threads in the backside of the arms to attach a chainring "carrier". The carrier would have holes at a much larger diameter, where the rings would attach, either both rings to the carrier, or the outer ring to the carrier and the inner to the outer. Could the 6-hole 116 BCD alloy rings have originally been designed to upgrade the old cottered steel cranks? It's been observed here before that the best quality steel crankarms of the 40' and 50's were often not much heavier than newer alloy arms, which are much thicker. But there would have been a significant weight savings in upgrading the steel rings to alloy ones. So were the 116 BCD 6-hole rings designed to bolt directly to the 116 BCD steel cranks, eliminating the carrier?

But the original bolts designed to secure the carrier would only be long enough for one chainring. Now the ring manufacturers could alway have supplied new bolts, and perhaps they did. But an option would have been to drill another set of holes to attach a 116 BCD inner ring to the outer one. Was anyone on the list working at a shop in the late 50's/early 60's, when this type of setup might have been introduced? Anyone have or have seen steel cottered cranks with alloy 116 BCD rings?


Jerry Moos
Big Spring, TX