Here you see the Saga complete bike equipped with the Ostrich F-104N handlebar bag, a smaller version of their best selling randonneur bag. These are slightly narrower which is ideal for bikes with higher trail geometry.
The bag can either be attached directly to the bars using the included leather straps or to a decaleur as pictured.
The Tanaka Decaleur pictured here allows for vertical adjustment to fit different size head tubes and bags. By rotating the cylinder back as pictured, you can increase the tension on the bracket pins to keep the bag from jumping up when riding over unpaved or poorly maintained roads. When the bag is lifted off the rack the tension is released and the bracket slides smoothly free of the cylinder.
For more technical offroad riding it's wise to strap the bag to the decaleur and the rack.
The Ostrich bags include a nylon quick release strap and an additional leather strap like the ones for the handlebars. I recommend using the quick release around the bracket and the leather around the rack tombstone. The bag can also be mounted on the bottom, but mounting it to the tombstone works better to prevent the bag from bouncing when the bag is empty or lightly loaded.
An issue I've encounter with some steerer tube mounted decaleurs is that they have a tendency to get pulled to the side by the weight of the bag. The Tanaka Decaleur addresses this by using a locking headset spacer to clamp it in place. The design is based on a seatpost clamp, so it's very secure.
They can also be mounted to bikes with 1" thread less steer tubes or quill stems using the appropriate width shims.
The 104N comes pre drilled for a decaleur bracket, but the Tanaka Decaleurs also allow the bag to be attached to the bracket with the handlebar straps for added security. The Ostrich bags have an internal metal brace which the straps loop around.
We've tried these decaleurs with a few different bags including the Swift Industries Randonneur bags, and we've been very satisfied with their performance. As with all racks, it's important to check that all mounting hardware is tight before every ride. Installing the mounting screws using blue thread locker is a good policy. Also remember not to over load your handlebar bag to avoid wheel flop at slow speeds. Handlebar bags should always be secured either to the handlebars or a decaleur in addition to the rack. For heavy loads a Pourteur style rack such as the Soma or Gamoh models will be more stable, and distribute the weight across a larger platform. Another excellent option is the Wald 257GB basket rack which can be mounted to the handlebars and axles of most bikes.