Froome and his bike have been photographed during this Tour with Osymetric's 110 outer chainring, which has 52 teeth. But apparently the "Osymetric" lettering has been covered or removed to avoid conflicting with Sky's Shimano sponsorship agreement.
The inventor, Jean-Louis Talo, is an engineer from France.
Team Sky boss Dave Brailsford has worked with Froome on "marginal gains," a performance philosophy he used with former Tour winner Bradley Wiggins.
Wiggins rode Osymetric rings when he won the 2012 Tour.
One of the first big-name pros to use Osymetric rings was American Bobby Julich.
If Froome, a Kenyan-born Briton, can keep his leader's yellow jersey until Paris this Sunday, he'll become the first British rider to win three Tours de France.