The Bontrager Adventure Boss frame bag is available in six sizes. It's designed to fit a wide range of bikes, but also has specific sizing and attachment features to suit the Trek Checkpoint. It might work brilliantly on the Checkpoint, but for other bikes, there are a few comprises.
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Within the Adventure bikepacking range from Bontrager are a seat bag, handlebar bag, and this frame bag. The other bags in the range are a general fit, but the frame bag has some elements designed specifically for the Trek Checkpoint. However, it can still be fitted to other bikes with alternative attachment points provided. I tested the 1.7-litre bag, the second smallest in the range (to fit the 52cm Trek Checkpoint). Having thumbscrews as fitment options, and sizes specific to frames is something we tested with the Cutthroat and in that instance, it worked very well.
The bag is constructed from water-resistant fabrics, and it has a waterproof zip to help keep the water out. To fit to a Checkpoint, there are thumbscrew attachment points around the bag (not included). To fit to any other frame, there are three buckle clamp top tube straps, plus a deep velcro strap to attach to the downtube. All the straps are removable which offers a cleaner look if you're just using the thumbscrew attachment points.
I had the bag fitted to a few bikes, including a medium-size mountain bike, and it fitted nicely within the frame. I had just enough room to have a small water bottle cage on the downtube. The attachments you would use on a standard bike are quite bulky, and while they give a secure fit, the size makes them awkward to attach and tidy the ends.
To fit the bag to Trek Checkpoint, there are three holes for the thumbscrews on the top tube, and further single connection points on the downtube and seat tube. The locations for the thumbscrews are small open holes, with no cover when they are not in use. While they do sit under the downtube, heavy rainwater has the potential to enter the bag, which is not ideal. The zip has a large, easy to grab puller and is easy to open and close. While the zip is waterproof, the zip garages are small, and I found often left a small gap, giving another potential entry point for water.
The bag has two pockets, one on either side of the bag, with the larger main pocket on the left-hand side. It is a simple open pocket with a few velcro straps to attach a pump, or perhaps shorter tent poles. On the right-hand side, the pocket is narrow, with a few slim compartments, and a clip to attach something to, such as keys to ensure they stay in the bag. There is no cable port or access point of any kind unless you potentially use one of the thumbscrews if they are not being used.
The Boss frame bag costs £95, which is similar to other high-spec, and well-reviewed bags. The Ortlieb frame-pack is £115 but is truly waterproof and very durable. For cheaper options, the Lifeline Adventure Frame Bag might be very simple, but it is only £25, and the Birzman Packman Travel frame bag that Ty recently tested is another cheaper option at £37.
Without having a Trek Checkpoint to test the bags on, it is difficult to give an indication of fit and performance for that frame, although the bag quality still doesn't match up to many other frame bags. When fitted to any other bike the attachment points are lacking, with multiple holes where water can easily get in. If you have a Trek Checkpoint and want a perfect fit and clean-looking frame bag it might work well, but for all other bikes, there are better and cheaper options.
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