Bike Rack Bag Pannier Backpack NICK 17-35 Liters . The bike rack seat bag is made of strong, water-resistant, durable, carbon composite leather. Because of the foldability, you can use the rack bag as a trunk or cargo bag. The bicycle bag rear rack can be unfolded with zippers to a bike pannier when you need more capacity. It is easy to install, steady, and convenient. It comes with a large 35L capacity, which can meet your needs.