Last weekend with 4 friends we biked from Burlington Vermont to Portland Maine on the Cross Vermont Adventure trail and Cross New Hampshire Adventure Trail. Second night in Jefferson, NH the temps dipped to 30 degrees. We woke up to frost on the tent, ground and our bikes (see pic below). We all had summer sleeping bags and everyone felt it haha. So, I'd say bring a bag for spring or fall (20-30 degree)
Frost on the front bag and saddle