Sonoma County is a perfect place for bicycling. Some roads like West Dry Creek have little or no shoulders, making them somewhat unsafe. Try to stick to the roads with decent shoulders, like Dry Creek Road.
The weather is usually perfect for bicycling. It is generally balmy year-round, except for a couple of hot months in summer and some rain in the winter. Humidity is low. The scenery is fabulous. The best part about bicycling here is the ability to stop at a winery for wine tasting enroute!
Little known fact: In California, it is a misdemeanor to operate a bicycle under the influence of alcohol or drugs. Having said that, I don't know of a single person who has ever been arrested for DUI on a bicycle. Nonetheless, please exercise caution. Sometimes, the drivers in cars can be very unaware or just plain reckless. And keep in mind - this is the wine country, so some of those drivers will be over the legal limit for alcohol. As a bicyclist, you just need to be on guard at all times, tipsy or not.
Equipment: Either a mountain bike or road or racing bike will work. There are not a lot of unpaved roads - most routes are on the paved roads with shoulders. Some wineries (but not many in Sonoma) have unpaved roads to their tasting rooms, which is why, between my mountain or road bike, I'll usually take the mountain bike.
The California Bicycle Helmet Law applies only to people 18 years and younger. Personally, I think it is insane to ride a bicycle on any California road without a helmet, particularly if you are sharing the road with automobiles and trucks.
- Wine Tasting