I've used a set of
Rotor rings for a round a year now. After a few weeks getting them set correctly for my pedalling style, and my legs getting used to the feel, I love them. It's hard to give a number as I'm not a record keeping/training/Time trialling kind of rider, but they're definitely an improvement is average speed...5-7% maybe? Mind you, that's still only 17mph over 16mph.
Yes, your feet still go around in circles....the idea is that the leverage/gearing changes as you pedal. A higher gear where you have most power, a lower gear where you have least power available. The Rotor rings are only 15% eliptical, nothing too weird.
IMHO Biopace was a rubbish idea that tarnished elliptical rings, even now 25 years later...the alignment of the rings was totally wrong. Look where the high spots are:
The idea was that the drop in gear as the pedal moved past TDC accelerated the leg and thus gave a little more kinetic energy to get past the dead spot at the bottom. It didn't work for me, on or off road, and smooth pedalling was almost impossible. I rotated my rings 1 hole clockwise. This improved things a lot.
Wiggins uses the slightly different
Osymetricrings. These are fixed position, quasi-square rings from France, with a big high/low difference. They claim a 10% wattage gain, so approx 3% speed gain. They look pretty extreme to me...God knows what the front shifting is like...
Sadly Chris Bell isn't making Egg Rings any more. His fight with prostate cancer has understandably taken priority, but the
Highpath website still has a good roundup of elliptical history.
L-shaped cranks made the same claims...but they were just b*ll*cks.
Rotor's cranksets are OK, but pricey. Just get a set of rings to fit what you've already got. The dealers should currently have a 'try them out' offer.
All the best,