This bag is designed to fit the long stride bikes (3C/8C/8S/11R) at the back section of the frame on the bottom. It has Velcro straps... Read More that affix around the frame tubing to keep it place. It is big enough to carry a lightweight jacket/shirt, or food, drinks, wallet, keys, phone, etc. It’s not large enough for grocery items or a computer (maybe a tablet). This bag is not waterproof, but does protect from light rain/splashes.