Around here (the Puget Sound area) most of the roadside political campaign signs are 24 inches long by 18 inches high and made from a material called coroplast. I wait until a day or two after an election and then go out and harvest the leftover signs and recycle them into bicycle fenders. While these fenders may not look very fancy, they work real well and are very light and inexpensive. This brief report should give you all the information you need to make your own set of fenders.
Coroplast is a plastic material similar in construction to the corogated cardboard used in making cardboard boxes. Because it's plastic, it's weatherproof, light and extremely tough. It's easy to cut and work with once you learn a few of the basic tricks. Coroplast has a "grain" formed by the internal corogation flutes. It is easy to cut if you cut along the flutes and if you want to bend it into smooth curves make sure you curve along the flutes. You want to make sure that the sign you get has the flutes running parallel to the long (24 inch) edge.
To make a set of fenders, you need the following things:
Materials:
1 -- 24 inch by 18 inch coroplast campaign sign.
A few dozen -- 8 inch nylon zip-ties.
You should be able to scavenge the sign from the side of the road (wait until after the election has passed) and you can buy a bag of 100 zip-ties for less than $5 in the electrical supplies department of your local hardware store.
Tools:
I make my fenders using just a Gerber Multi-Plier 400 but if you want to use individual tools, the following are helpful:
Once you have the materials and the tools, set your bike up in a comfortable place and go to work.
First off, you need to cut your sign into a bunch of 24-inch long strips. You'll need 8 one-inch wide strips and 5 two-inch wide strips. The two-inch wide strips will form the actual fenders and the one-inch wide strips will be the fender stays. As I said above, cut with the grain of the flutes. The dimensions don't have to be precise and in fact you may opt to make your fenders narrower than two inches (or wider if you're making fenders for a mountain bike). But it's harder to make real narrow fenders, so I recommend two-inches as a good starting point. If you try to make wider fenders, you'll need more than one sign. But with two-inch wide fenders, you can cut the sign like this to get all the strips you need:
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Once you have all the strips cut, we can begin shaping them into fenders. The basic building technique in building up the fenders is a sequence that is repeated with each piece. The sequence goes as follows:
Let's start with the back fender. Take one of the two inch wide strips and TEST fit it between seat tube and the rear tire. One end will rest just above the bottom bracket while the length of the strip will travel up along the seat tube before curving back to go between the seat stays and point to the rear of the bike. Here's a picture of a completed rear fender, so you have an idea where all this is going:
Now at this TEST stage, you've probably figured out that the two inch wide fender doesn't fit between your seat stays. And you have to figure out how to get around the rear brake. And you may have problems clearing the front derailleur (not an issue on the bike in our photograph since it's a fixed gear and doesn't have a front derailleur). But that's the reason for doing the TEST. The TEST tells you what you have to TRIM.
In the TEST stage, you'll have to figure out how you are going to make a certain piece fit on your bike. In the case of the bike in the photograph, there is very little room between the rear tire and the rear brake. Conventional fenders always try to squeeze into the area between the tire and the brake, but one of the advantages of making your own fenders is that you aren't bound by convention. If you look at the photograph, you'll see that I routed the fender over the rear brake. This gives you the maximum amount of tire clearance, although it doesn't protect the brake from road grime like a conventional fender does.
No matter if you go over or under the rear brake, you will probably have to TRIM the coroplast to fit between the stays. You may also have to TRIM things to clear your front derailleur or chainrings as well. I usually mark off what has to be cut and then TRIM the coroplast with a sharp knife blade.
Once the piece has been trimmed into shape, you'll have to PUNCH a few holes in the coroplast. You'll route zip-ties through these holes and the zip-ties hold the fenders to the bike and are also used to STITCH the various pieces together. In the case of this first piece, you'll need a set of holes for the zip-tie that holds the front edge of the fender to the seat tube just above the bottom bracket. You'll also need some holes for any zip-ties that hold the fender to the seat stays by the rear brake. You'll also need a couple of holes for any zip-ties that will be used for stitching on the next piece.
By now you may be very confused. This is normal. The problem is that bikes come in different sizes and I can't give you a one-size-fits-all set of instructions that says something like "punch a hole one-inch from the end of this piece". What I can tell you is to look at the pictures, look at your bike, and try to use what I've done as guidelines for your own fender project. What I can tell you is that a small, sharp-bladed screwdriver is very good for punching the zip-tie holes. And that you will use the zip-ties in place of nuts and bolts to hold the fenders onto your bike. You will also use the zip-ties to STITCH the various pieces of coroplast together. Take your time and think of this as sculpture. You are creating a set of fenders and coroplast and zip-ties are your raw materials. You will cut and shape and stitch these materials into a set of fenders. If you get something in the wrong spot, you'll figure it out pretty quickly. In the worst case, you may need to start over with a new piece of coroplast or unsnip some zip-ties. But if you follow the basic sequence of TEST, TRIM, PUNCH, FIT, and STITCH, you will probably be fine.
I've already talked about TEST, TRIM and PUNCH. Once you've trimmed everything and punched the proper holes, your piece of COROPLAST should FIT right where you want it. When you're sure it's in the right spot, use zip-ties to STITCH it in place. Once you cinch the zip-ties in place, you can trim off the excess. I use the term STITCH deliberately, especially in reference to joining coroplast. Coroplast is a very versatile material, but it is slippery and materials like many glues don't bond to it. But by using two zip-ties and overlapping the ends of a couple of pieces, you can join them together to make one longer piece. Here's an illustration:
Take two pieces and punch some holes
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Slide the ends together so the holes overlap
and stitch things together with zip-ties
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and you've got a longer piece of coroplast
Now that you have the first piece of coroplast in place, things will go quicker. You'll need to stitch a couple more of the two inch wide pieces to the back of your existing piece to form the rest of the fender. You probably wont need the full length of both pieces, but you want to make sure your fender extends far enough down in the rear. You can save some of the extra coroplast and when your done you can use it to craft a little rear flasher bracket like the one shown in the photograph. Until you put the rear fender stays in place, your fender will just stick straight out from the back of your bike, so your next step is to get those stays in place.
The stays are made from the one-inch wide strips you cut earlier. You make the stays by taking four of these strips and scoring a crease one inch from one end.
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This crease runs across the grain of the coroplast and the best way I've found to make this is to use a ruler and something pointy but not real sharp. The tip of a Phillips screwdriver works well. The idea is to score a crease that will let you put a right angle bend in the coroplast, but not to break the surface of the coroplast and expose the flutes. Once you make the crease, bend the one-inch section up so it is at a 90 degree angle to the rest of the strip. From the side, it will look like this:
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Now that you have the ends of the stays bent, punch holes in the bent ends. Test fit the stays to the fenders and punch corresponding holes in the fenders in the right spot. The photograph illustrates where the stays should go. For now, don't worry that the stays may be too long. Stitch the stays to the fenders with zip-ties.
With the stays attached to the fenders take the pair of back stays (the ones that will run parallel to the ground) and figure out where you'll need to punch the zip-tie holes for attachment to the rear triangle of your bike. If you have fender eyelets on your bike you can route the zip-ties through the eyelets, but if not you can wrap the zip-tie around the seat stays. I usually use a couple of zip-ties on each side to make sure things are secure. Once you know where the holes are going, you can trim of any excess length of the fender stays. Once the back stays are in place, do something similar to get the vertical stays in place. Once you snug the last zip-ties in place, your rear fender is done. The coroplast may flex some, but if you've done everything right it shouldn't rub anywhere and will provide you with years of protection from road spray.
The front fender is constructed along the same lines as the rear fender. In the case of the sample bike in the photograph, the front fork doesn't have fender eyelets and there is minimal clearance between the fork and the tire. As you can see, I routed the fender over the brake and fork crown. This required making the front fender in a couple of pieces and stitching it together with zip-ties.
Front fenders are a bit trickier to get right than rear fenders. You don't want the fender to extend to far back or it will overlap with your toes or it may even hit the downtube. On the other hand, you have to make sure the fender clears the tire. The diagonal stay is critical in keeping everything in proper alignment.
Like you did with the rear fender, use zip-ties to attach the front fender stays to the bicycle. In the case of the front fender, the zip-ties also serve as a safety device. While zip-ties are strong, in the unlikely event of a stick or some other hunk of road debris getting kicked up and caught between your fender and your wheel, the coroplast will deform and the zip-ties will probably snap. This is far preferable to having your front wheel lock up!
That's basically it. While these general instructions and pictures describe making fenders to fit a road bike, I've made similar fenders for recumbents, folding bikes and mountain bikes. As with any do-it-yourself project, apply some common sense and make everything is secure before you ride. And some zip-ties do degrade over time with exposure to sunlight so check them periodically. But make yourself some fenders and you'll find rain riding is much more pleasant.
I'll see you on the road,
Kent Peterson
Issaquah, WA USA
March 15, 2002