Elliptical chainrings have been around since the beginning of the bicycle.
Elliptical bicycle crankset.
The premise is simple.
By using an oblong rather than circular shape you can effectively make the chainring.
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A growing trend in cycling is the oval chainring also known as an elliptical chainring.
That shimano manufactured an elliptical chainring in the 1980s called the biopace and aside from a few love letters the component was generally panned for causing undue stress on the knees.
Biopace biopace is a patented non round chainwheel design made and licensed by shimano.
This unique piece of gear is gaining popularity among road cyclists mountain bikers bicycle tourists and commutes.