Chris Bell - Oval EGGring Notes

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Durham chainring

52t Durham chainring (USA, 1970's)

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Here are some examples of Oval chainrings that have been made during the past 125 years:

decade introduced	name	origin	shape (*)	size (*)	ovality (*)	crank offset (*)
1890	Linley + Biggs unknown	UK	joined semicircles ellipse		adjustable 30%	0°
1920	Lantier	France	rough ellipse	48	40%
1930	Elan Thétic van Deuren	France Belgium Netherlands	rough ellipse ellipse ellipse	48 46	40% 15% 11%	0° -37°
1940	Larsen		trimmed rhombus	50	54%	0°
1960	Bridgestone	Japan	ellipse		6%	+24°
1970	Daniel Durham Polchlopek	France USA France/NL	ellipse joined semicircles	52 48	28% 65% 23%	+30° +15° -12°
1980	*Biopace types ()** Shimano Biopace Miche Ofmega SIO SR Ovaltech Stronglight Sugino Cycloid	Japan Italy Italy Japan France Japan	rounded rhombus rounded rhombus ellipse ellipse ellipse ellipse	28 28 28 48	16% 16% 17% 8%	+50° +50° +74° +90°
1980	Mavic EGGring	France UK	skewed ellipse ellipse	26 custom	13% custom	adjustable custom
1990	Harmonic MPS	Monaco Ukraine	bi-radial ellipse	54 40	21% 31%	-3° -35°
2000	Osymetric Rotor Q-ring	France Spain	bi-radial ellipse	52 53	21% 11%	-3° adjustable

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(*) Shape:: The different shapes have little effect on how the chainrings work in practice. An ellipse is the purest shape from a mathematical point-of-view and, arguably, gives the smoothest transition between major and minor axes, but some of the other shapes are easier to design and make. It has been suggested that the shape of Biopace chainrings owes more to its patentability than to any performance benefits.
(*) Size, ovality and crank offset:: Most types were also made in other sizes. The quoted ovality and crank offset relate to the example size given.
(*) Biopace-type rings:: These gave Ovals a bad name in the 1980's because their crank offsets orientated them back-to-front on upright bicycles. This gave a higher gear to push through the dead-spots instead of a lower one, making matters worse, not better!

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EGGring Oval Chainring Notes