Bike saddle bags
Attached under the saddle and along the seat post, the saddlebag carries repair essentials without a rack, and fits bikepacking format on rolled models. From the tool case to the long waterproof bag.
A saddle bag attaches under the saddle and along the seat post, without needing a rack or drilling into the frame. Compact models carry a spare inner tube, tyre levers, and multi-tools all the time. Longer roll-top models are used for bikepacking and can replace a rear rack on multi-day trips.
Choosing your saddle bag based on the volume to carry
There are two main types. The small zipped pouch stays attached with the spare tube and multi-tool: you forget about it and it comes in handy when you get a flat. The long roll-top bag compresses, is adjustable in volume, and is enough for carrying a light sleeping bag or three days' worth of clothes. With a road bike saddle bag, the deciding factor is the clearance between the bottom of the bag and the tyre when the seat post is not extended much. Measure this clearance with the saddle set to your height before ordering.
Attachment, stability, and waterproofing of a saddle bag
Three systems are available on the market. Velcro straps can mount onto any rails and can be removed in a matter of seconds. Rigid clip attachments eliminate swaying, but require a support to be left in place. Rubber straps with buckles hold well on rough terrain. A bicycle saddle bag that swings around will eventually rub against the tyre and wear out its fabric, so re-tighten it after your first rides. For winter, a waterproof saddle bag made from welded fabric and roll-top closure offers better protection than a cover added on. On muddy trails, a gravel saddle bag should mainly be easy to clean, as the rear wheel will spray dirt onto its underside.
Compatibility of a saddle bag with saddle rails and dropper posts
A well-chosen bicycle saddle bag takes into account two mechanical constraints. The carbon rails of some saddles prevent the use of a rigid clamp, as indicated by the manufacturer in their instructions. A mountain bike dropper post significantly reduces the available height in the lowest position, which rules out larger bags and directs you towards a flatter model. Also consider the rear light: many models have a loop for it, otherwise the light may end up positioned on the post or helmet. Ortlieb, Topeak, and Restrap each cater to different uses, from waterproof pouches to strapped bikepacking bags.
