Introduction: Bicycle Pannier Bags From Shoulder Bags / Satchels
These pannier bags are permanently and securely attached to the carrier rack. A liner bag can be used which you can take with you when parking your bike. The liner bag could be plastic if your bags need waterproofing.
I didn't make the bags - I bought them from a charity store. They were originally a shoulder bag or satchel with a shoulder strap, which was removed. You really don't want any loose straps hanging from pannier bags, because if they get tangled in your wheel then down you go...
I fitted a rigid plywood panel to the inside of the bag and bolted on straps which wrapped around the carrier rack tubing. The rigid panel stops the bags flexing and getting caught in the spokes. A wide surface on the side of the carrier rack itself will also help prevent bags flexing into the spokes. Take all precautions to prevent the bags getting caught in the spokes!
Make sure the bags are mounted far enough back that your heels don't hit them while pedaling.
Step 1: Making the Straps to Tie the Bag to the Carrier Rack
The straps were cut from bracing strap. The large holes in the strap are 6mm wide and 35mm apart, which ended up being the perfect spacing for wrapping around the carrier rack tubes.
Use tin snips to easily cut the strap into shape. Cut off the corners and file them smooth. This makes it easier to handle and it won't tear your bag.
Fold the piece of strap around your carrier rack tubing to shape it, taking care to fold it exactly in the centre so that the holes line up. In this case the centre is where the small hole is.
Step 2: Cut Your Plywood Panel and Drill the Holes
I used a piece of 3mm plywood to make the panel. An offcut of bracing ply can often be salvaged from a building site skip/dumpster.
Cut the plywood to fit inside your bag and glue it in position. The glue will strengthen the contact between the bag and the ply. I used a polychloroprene contact adhesive. Once the glue has cured, hold the bag against the rack and mark out where the holes will be for mounting the straps.
Drill these holes to 6mm or 6.5mm. You may want to drill and bolt the top two straps first before marking and drilling the bottom hole, because it needs to be fairly precise. Hold a block of wood inside the bag for the drill to run into as it penetrates the ply, otherwise you'll end up with a hole in the other side of your bag.
Step 3: Secure the Bags to the Rack With the Straps
Bolts with wide flat heads were used - 30mm long with M6 threads. Get the top two straps in position on the carrier rack. Push the bolts through the holes in the bag and ply panel, and then through the strap holes. Secure with nylock nuts. Now fit the lower strap in the same manner. Remove the rear wheel from your bike if you need better access.
Only tighten the nylock nuts enough that the straps don't wiggle around.
Step 4: Test for Bag Flex, Test for Position
Once the bag is secured, test that it doesn't rattle around; test that the straps are fitting tight enough on the rack.
Also test that the back lower corner of the bag doesn't flex too much. Just give it a gentle flex, or fill it with some heavy stuff you may want to carry (e.g. cartons of milk) and wobble it around. It should be at least 5cm/2inches clear of the spokes.
Ride the bike and check your heels don't hit the bags.
Once it passes these tests, it's good to go!
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