Joined: Feb 2013
Posts: 1,472
Likes: 11
From: Near St. Louis, Missouri
Bikes: Giant Defy Advanced, Breezer Doppler Team, Schwinn Twinn Tandem, Windsor Tourist, 1954 JC Higgens
It's a typo. I counted 7 gears on the cassette and 3 chain rings. That's a 21-speed in my book even if some are duplicates.