Unusual elliptical chain ring

[blackhawknj]

Interesting. There was some interest in elliptical/out of round chain rings in the early 1980s, I recall one woman member of my club said they helped to eliminate knee discomfort. IIRC people found out they could not be used with a derailleur and their benefits were "greatly exaggerated".

 

[dnc1]

Juvela ,dull braine? you are like a walking encyclopedia your lightweight knowledge is incredible many thanks for your contributions. Brian

Ditto, cheers @juvela !

 

[1951 C.W.S]

what would be the use of something like this?

 

[bikejunk]

My 1893 Columbia had an elliptical sprocket and yes back in my racing days in the 1980s we had Bio-pace elliptical sprockets . 1951 C.W.S they supposedly give you a mechanical lever action advantage over a round chain ring - I found the messed up my perfect circles in a sprint

 

[juvela]

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Here upon the puddle's occidental margin we have had some aftermarket non-round chainwheels offered from time to time.

One recalled from the mid to late seventies era was the Durham. For several years there each time an enthusiast opened a cycling periodical there would be a mailorder advert from Durham.

Theirs were done in dural. One problem for these cottage industry operations was the decision as to what drillings to offer. Since they were done on a small scale more than one drilling option would shoot up the overhead...

Here are two models of Durham's from BITD -

for three-arm 116mm BCD:

https://flic.kr/p/izaUfd

https://flic.kr/p/iy6rrX

for five-arm 144mm BCD chainsets:

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[dnc1]

My friend is in the process of fitting it to a bare steel '30s Hercules sports bike, I'll post pictures when I have them.
I came across a few of those 'Durham' chainrings @juvela, whilst searching for info on the Elan example.
Interesting that this idea keeps recurring through the ages. As @bikejunk implies above, a probably very sound idea on paper that proves less so in actual use,
By the way @bikejunk, do you have any photos of the version in your 1893 Columbia?
I'd like to see that.

 

[Cowboy in NC]

I had a similar skip tooth sprocket years ago---sold it on Ebay. Someone here on the Cabe bought it- because they posted a picture of it . It was called a "Rock-o-Matic Rocket Sprocket, circa the 1940s. " Maybe they will see this and repost or maybe someone will look it up.
God Bless,---Cowboy

 

[New Mexico Brant]

I believe this to be a 19th century Columbia version:

 

[dnc1]

Wow @New Mexico Brant , that almost looks homemade. I wonder how it feels in use?
Very cool!

 

[juvela]

I believe this to be a 19th century Columbia version:

View attachment 1069336

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Wow indeed!

Shape looks a dead ringer for the Bernard Hinault:

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