Love at first sight! Unfortunatly, after about a month of hard use on the training course, one of the zip ties pulled through the thin plastic of the jar (it's all good, I wanted to "upgrade" to a bigger jar anyway). This led to a little design-tweeking, and this instructable.
Things you will need:
- A clean, empty plastic jar. I'm a fan of the 28oz peanut butter jar, but any plastic jar with a wide mouth and screw-on cap will do.
- 2 smallish zip-ties or cable ties
- 4 washers (I used 1/8 x 3/4 fender washers here, but I originally used miss-matched washers and it worked fine)
- a big nail, awl or small drill
- a hammer (not necessary if using a drill)
- duct tape
- Bike in need of a saddle bag
- reflective tape (optional)
Make sure your jar will actually fit under your saddle! Tall people are probably fine here, but I'm pretty short and my seat is pretty low. You may notice in my photos I actually had to take my rear reflector off (I'll re-mount it later). You don't want a jar that can't fit between your rear wheel and your saddle, nor one that's so big your legs touch it when you peddle. On the other hand, it should be big enough to hold things. The jar in the pictures is actually a smidge too small to hold everything I wanted (spare tube, tire levers, patch kit and multi-tool), but I don't know what you are going for. Try packing the empty jar once before mounting it, to be sure it works for you. Again, I recommend 28oz peanut butter jars :-)
Hold your jar under your saddle, against the two metal bars that attach your saddle to the seat post. This is where you will ultimately attach the jar. Use your marker to mark on the jar, where the edges of the bars touch the jar. In total, you will have two sets of two marks. You may need to just mark the outside marks and then eyeball for the inner marks.
Punch 4 holes in the jar. You will reduce the chances of the plastic tearing if you can make the holes round, so I advise against using a blade. I used a big decking nail and gently hammered until it punched through the plastic, then kinda twisted it around in the hole to widen it and smooth it out. An awl or small drill would probably give you an even tidier result.
Thread in the cable ties and washers. First insert a cable tie through a washer then into an outer hole, with the female (open) end pointing outward. Inside the jar thread a second washer onto the cable tie, then thread the 'tie through the inner hole on that side. Your end result should be the cable tie bent in a "U" with both ends outside of the jar, one washer flat against the outside of the jar and one flat against the inner surface of the jar. Pull the cable tie pretty tight so the washers lay flat. Repeat on the other set of holes, making sure the cable is a mirror of the first, so the female side is facing out on both.
Place a rectangle of duct tape on the inside of the jar over each washer. You don't need a ton of duct tape, just enough to cover the washer and holes on the inside of the jar. This keeps the washer in place, and stops stuff from catching when you pull your gear in and out of the jar later. It also stops grit and water from leaking in through the holes.
Mount the jar on your bike. Thread the ends of the cable ties through your saddle bars, going from inside to outside, and loosely pull them through the female ends of the cable ties. When both sides are set, tighten the cable ties as much as you can. Load that puppy up and head out!
You can trim of the ends of the cable ties if you don't like having them visible. I kinda like it. Also, if you are blocking or had to remove your rear reflector in order to mount the bag, you'll want to slap some reflective tape on the jar to make up for it. Also if you need to use up a whole jar of peanut butter to do this, this is my favorite peanut butter cookie recipe: http://allrecipes.com/recipe/quick-peanut-butter-cookies/detail.aspx