All you Californian mountain or road bikers, we are planning to be in the Napa Valley for a couple of days in late May. Is it necessary to book a one day bike tour with a professional company, or should we just head out with a map on our own? We would like to stop at a couple of vineyards and get some exercise along the way. We are decent but not professional bikers and can manage some hilly terrain. Probably just want to go 30-40 miles/max for the day, allowing plenty of time for eating and soaking up the ambience. Any help appreciated.

Why not consider cycling in Sonoma County for at least one of those days. You could do a looop from Healdsburg, out Westside Rd..connecting to Eastside Rd. and back into town...or along Dry Creek Valley or around the Alexander Valley. Each of those routes passes great wineries and will give you the chance to stop and taste. You might call the Healdsburg Chamber of Commerce and see if they have a map of bike routes they could send you.

Have a great ride! You certainly can do it on your own. Do be aware of roads that cross RR tracks; some riders have snagged their tires in the tracks and have gone head-first to the pavement. Just be mindful of this and you'll enjoy your scenic travels.
You could also call St. Helena Cyclery (in St. Helena, Napa Valley) and they are sure to give you advice re. maps and/or guides.

Thanks for the information re: Chamber and St. Helena Cycling. I'll try both. Are the roads heavily trafficked mid-week?

If you want an interesting choice of places to stay in Hbg where your bikes would be safe...check out www.sonomacountyvacations.com. Rentals towards the end of the list are less expensive.