Backpack Pannier Conversion Kit (No Fasteners)

Motivation

I wanted to use my backpack as a pannier on my bike rear rack and found a few solutions online that involve drilling through the backpack strap or bolting some clamps to the straps. I wanted something that wouldn't require additional hardware and that was detachable. Additionally, I found when experimenting that having a rigid handle connecting the parts that hooked onto the rack was much more convenient for taking the backpack on and off the rack, so I included that in my design.

I also wanted to experiment with snap-fit designs, which I ended up using for both connecting the hook and clamp pieces to the main handle piece.

Important note: I have used this system on my bike for a few weeks now for groceries, and have not had any issues. However, I haven't put more than ~15lbs in the backpack, and I wouldn't use this system to transport anything too valuable or heavy.

Important note: It is important to have something that will keep your backpack straps out of the way of your rear wheel spokes when using this system. I have found using bag clips to cinch the straps together or something similar to be a pretty effective way of doing this.

Details

For one backpack, you will need:

• 2x hooks
• 2x clamps (ie. 55x2.5 means 55mm strap width, 2.5mm gap between clamp and handle)
• 1x handle (ie. 140x55 means 140mm between strap centers, 55mm strap width)
• It is necessary to match up the first number in the clamp name with the second number in the handle name.

There are multiple sizes of clamps and handles, but the hooks are one size fits all (ie. as long as the bike rack tubes are 10mm diameter). To choose the right sizes:

• Measure the distance between the centers of the straps on your backpack at the point you intend to hang it from, and choose the size of handle whose first number is closest to that measurement (in mm). If none of the handle sizes fit, you can use a slicer or other modification tool to remove the actual handle part of the handle so you will have 2 independent hook/clamp assemblies.
• Measure the width of the backpack straps. If they are 50mm or less, choose handles labeled “x55”, and if they are wider than 50mm choose the “x70” ones.
• Measure the thickness of the (uncompressed) backpack straps. If they are about 5mm or less, choose the clamps labeled “x2.5”, if they are thicker than about 5mm choose the “x5” ones (this depends on how squishy your straps are, so some experimentation may be necessary).
• If you intend to still use the backpack as a backpack with the conversion kit installed, I recommend placing them as high as you can, which is usually a few cm from where the straps connect to the pack. You may also want to choose a wider handle if you have broad shoulders so the straps can spread out more when you are wearing the backpack.

Printing Tips

• I have only tested this system with ABS, and I wouldn't recommend using PLA because it's so brittle, but PETG might be reasonable.
• I built in some tolerances to the snap fit parts, but they are still quite snug, so you will need to dial in things like your extrusion multiplier and such on your printer.
• I printed this with 0.2mm layer heights, 4 perimeters, and 40% infill. The 4 perimeters are important to ensure the snap fit clips are printed fully dense.
• Supports are needed to print the hook pieces, so some cleanup may be necessary there to ensure good fitment with the handle.
• Recommended slicing setup is in the photos.
• Assembly and attaching/detaching instructional gifs in the photos.