I mapped a ride around the Lake with detours around most of 25 in Meredith, but I haven't done it yet. The traffic is a real concern for me, most of the roads are main drags. The Moultonboro cycle club rides just about every week during the summer and are a great bunch of people. They have a facebook page
http://www.facebook.com/group.php?gid=67170109800
I like to ride around Squam and the smaller lakes, about a 40 mile loop starting from the supermarket in CH. The roads are pretty quiet except for a few stints on 3 and 25B. Grandma's hill in Sandwich used to kick my butt, but not any more, it just hurts some now.....