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Unusual elliptical chain ring

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It came off of a heavy 10 speed frame I found in a junkyard 30 years ago, with TA aluminum cranks attached, so probably 1960s to 1970s.
 
I have one similar to the Durham, but with a double chainring. Since I don't even like Biopace rings I haven't put it on a bike. I have thought about turning it into a clock.
View attachment 1069693

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Thanks very much!

Looks to be the 50.4mm BCD.

Interesting that the maker provides the user with the option of two different mounting positions.

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I noticed that too. One seems to be marked "15" with a numeral one as an arrow, and the other "CR". I have no idea what that means.
 
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These two-plateau models make me jaw drop.

Can no imagine watching a front mech attempting to do its job... :eek:

A bit like asking Bambi to herd Godzilla.

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I think you would have to very careful when you made the change! Mine has a LOT more wear marks on the big ring than the smaller, 36 tooth ring.
 
Anyone have a pic of Mel Shorts bike with the Triangular ring?
Hannah Simpson has one as well, killer bikes with the offset from center rear cog to compensate. Crazee stuff


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Found this image of a Durham two-plateau arrangement with a drilling for the 86mm BCD.

Look at the wylde adaptation for a front mech! :dizzy:

Durham elliptical w:86mm BCD  .jpg


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