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Unusual elliptical chain ring

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Found this additional example of a Durham fitted to a three-arm 116mm BCD spider.

It even still has it paper label. No wonder so few of the labels have survived!

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Here is my friends Hercules with the chain ring installed.....
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He describes it as "like being on a cross trainer at the gym" in use. A bit bouncy and quite weird!
 
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Thanks for posting!

When I saw the small edition of the first image me thought was "wonder just how long that rear mech is going to last!" ... then saw in second image that is is not a mech but a tensioner. Sensible arrangement. ;)


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I finally saw Adam's Hercules in the flesh at the Benson VCC annual social evening last night.
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He kindly allowed me to take it for a quick spin around the car park at the venue.
It's an interesting riding sensation. It feels like there is a very, very small moment where you lose power; I can only liken it to the feeling of a hub gear slipping or, a loose crank/cotter pin as you push down on the power stroke.
He tells me it does seem to make going up hills slightly easier.
Will see how it fares when he's next able to come on one of our 25 mile rides.
 
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Thanks very much for this report and the additional images. The mighty Herc's frame appears to be in bare metal; does Adam have a coating on there to protect it from corrosion?

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Minor addendum on the Durham elliptical chainwheel -

Creator Roger Durham is also the person behind the Bullseye line of cycle products:

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I've told people over the years that I have been in the industry long enough for 5 iterations of oval rings.
Dates me for sure!!!!
 
I have acquired the 'Elan' chainring and cranks from my friend Adam.
Looking forward to finding some appropriate French period cranks and fitting it on my "new" Ciclos Minaco project.
 
Indeed a predecessor to the rather common Shimano Biopace of the 80s-only several shown here have a much more radical ellipse. The Shimano version is not immediately obvious to the eye or legs. As to the purpose, they are supposed to make it easier to turn when your legs are at the point of the circle where they can contribute the least force, as the available power of the legs builds so does the diameter of the ring--then the ends of ellipse engage during the power stroke. If you measure the distance between the points of the football, that's the effective diameter of the chainring--but should require the same energy as one several sizes smaller (if round). BTW mount your crank arms in the wrong relation to the ellipse and you're screwed.
I've never thought about it 'til now, but I wonder if it was named Biopace because it used the Golden Ratio -1.618 (or close to it). Anyone know?
 
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It was used apparently in 'Le Tour'.....
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I'll be trying it out with a period BSA flip-flop hub (fixed/free).
I'm in the process of modifying a very early Cyclo 2-speed derailleur to use in place of the missing "Galet".
 
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