Where are good places to go cycling on the weekends from Tokyo?
I'm thinking day cycles coming back the same day, as well as weekend cycles staying over at a B&B or campsite for a night or two. I also have a rinko bag to take my bike on a train (e.g. take a train to Kurihama, then a ferry over to Chiba and do a little cycling around there) so hopefully more spots to see. Anywhere to escape the concrete jungle for a day or so :~)
Chichibu is not that far off from Tokyo but is very un-city. It's easy to access Chichibu by train (from Ikebukuro, take the Seibu Ikebukuro line then change to the Seibu Chichibu line and take this all the way to the end). Fall is a great time to do this then you can enjoy the mountain's autumn foliage.
You can ride the full length of the Tama River on a good day -- all the way from the old water works up near Oume, down about 50km to Haneda airport where the Tama lets out to the sea. Most of the way on the north-east side of the river, there are either cycling tracks or parallel-running side roads with not too much traffic on them.
The best time of day to go is in the mid-morning, after the old people have taken their morning walks and the young ones are still buying lunchboxes at the conbini and making their way out to the area by train or bicycle.
Up at the Oume end of the river, there are plenty of mountains and hiking trails, so if you're not tired out from cycling, or if you brought a sleeping bag, you will have plenty of opportunities to do a stop over.
The Tama River along Ome Line is an ideal place to go on cycling. It will get you until Haneda Airport and the view is also breath-taking. I've been wanting to try that out since last Summer, but I never had the chance because I became pregnant then. Good luck!