Another great century to break yourself in on is the Wine Country Century, put on by the Santa Rosa Cycling Club. Very well supported--almost too well as one year I think I actually weighed more at the end of the ride then I did at the start. It's relatively flat (mostly rollers with a couple good climbs). It's an excellent route for tandems. The number of riders reached a peak last year and the popularity of the ride was threatening to ruin it so this year they aren't doing ANY advertising. If you're interested, you'll have to keep your eye on their website (www.srcc.com).