Introduction: Hack Your Messenger Bag to Make a Bike Pannier

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I have a couple of messenger bags that I don't use very often (coincidentally, i also live in San Francisco). After some doctor-says so, I decided to lighten the load on my back and shoulders so I converted the bag to a pannier.  The whole process took about 1 hour and cost me less than $30.  The project uses only basic tools and all materials can be found in your local hardware store.  The grommets are actually carried at my hardware store but if you can't find them, try a craft store.  I started by making only one pannier.  I actually find it very easy to ride with just one, even when it is weighted down.  You could always make a pair if you like feeling balanced.  It is also designed to be easy to snap on and off so you can carry the bag with you.  This is roughly based on other folks ideas but I tweaked it with the addition of grommets, rope clips, and the "chain quick snaps".  I've been using the bag for about a month and it is working perfectly.  Also, my landlord says I look cool.

Step 1: Materials

Materials: 

One messenger bag (re-purpose an old bag!).

3/4" Stainless steel machine screws (#10) - 2     $1.50 ea
#10 Stainless steel hex nut and washer- 2 - $0.50 ea
3/16" rope clips - 2     $0.88 ea
Grommet size "0" - 6     $3 dozen
Grommet size "2" - 2     included with grommet tool
Blue Hawk 3/4" Chain Quick Snap - 2      $7.00 ea
One bungee cord (24" length) - $1 
One key ring (about 1") - $0.20 
1/4" Plywood - 13.5" x 17" (may be smaller for some bags) - $5

Tools:
Saw (handsaw, jigsaw or bandsaw)
Hand drill and bits
Hex wrench
Grommet tool   

Total cost: $29
Obviously this would be cheaper if you already have some unused bolts or plywood in your garage. You could also save some $ by using a carabiner.



Step 2: Measure Your Bag

1. Your bag might look like mine or it might be a bit more squarish.  Either way, it doesn't matter. You'll feel just as self-satisfied.  Lay it down and measure across the top seam and the bottom seam like in this picture.
2. Grab your plywood and use a straightedge to cut a piece that approximately matches the footprint of the back of your bag. You don't have to be very precise here.  Your cuts don't even have to be pretty.  This is going to be on the inside of the bag.  A semi-famous man once said, "don't make your project into an anal retentive neurotic nightmare".  I try to keep this in mind when I am designing my projects.
3. Round the corners and test the fit.  This piece just needs to sit inside the bag to keep the back stiff when hanging on your bike rack.

Step 3: Prepare Your Bungee

1. Trim the ends off your bungee with a strong scissors, leaving a 24" piece.
2. Use a lighter to melt the ends so that they don't fray.  Be smart about fire.  This worked really well for my bungee which I think has some sort of nylon housing.  If you have a cotton-housed bungee, don't try to melt the end!
3. Measure the diameter of the bungee and make sure you pick a grommet that fits over it.
4. Tie a knot in one end and make it tight.


Step 4: Drill Holes in Your Wood Like So.

1. Grab your rope clips and trace little circles near the two plywood corners .  Drill holes so that the rope clips can slide in an out.   Mine were 1/4" diameter.
2. Drill two holes for your bungee to pass through (mine were 1/2").  Check that your bungee can fit through these holes.  The holes will be located about halfway down the length of your board.
3. Drill holes near the bottom two corners for your machine screws.  Make sure the screws easily pass through your drilled holes.   

Step 5: Trace Little Holes and Cut

1. Using your drilled wood piece, trace the holes onto your bag, holding the fabric taut.
2. Make small cuts in the fabric at these spots.  This is where you will place your grommets.  Cut the holes just big enough to slide in the grommets.
3. Insert your grommets and set them in place using your grommet tool.  There are many grommet variations.  The easiest for this project is the hammer-in type of grommet.

Step 6: Assemble Your New Pannier!

1. Pass the bungee through the grommet and plywood inside the bag.  Attach the key ring to the outside and loop the bungee back through to the inside of the bag.  Pull as tightly as you can and tie the other end on the inside of the bag.  The bungee should be taut but stretchable.  This loop is going to attach to your bike rack at the very bottom.
2. Insert screws and rope clips with "Chain Quick Snaps" in place. Tighten on the inside of the bag.
3. You are done!  Now snap it on and go get some groceries! (and look cool doing it!)