Bicycle fender made from a plastic jug

Step 2 Cutting the fender

Now that you have a jug, some scissors, and some tape let's get to it. First, take the scissors and cut around the jug to get the vertical portion of the plastic. The idea is to cut the top and bottom off, and then cut this hoop so that you have a nice long flat rectangle of plastic to work with.

Next, draw your fender pattern on the plastic. The keys to sizing the fender is to make sure it is wide enough to cover your whole tire and long enough to keep spray from whipping off the rear of the tire up onto your back. My fender is 4 inches wide and about 24 inches long. This is pretty long as you can see in the pics. You can trim the fender afterwards if desired once the spray pattern of your specific tires is characterized. Spray comes off of your tires tangentially, so if you look at the layout of your bike you can see how long your fender needs to be to keep spray off of you in the saddle.

My fender (below) includes some notches on the sides for clearance of the side bars on my bike rack. My pattern also includes a pair of slots in the middle and a slot at the front to allow the fender to be taped and zip tied to the rack. Your pattern may differ and could include provision for mounting to a different type of rear rack, a support structure of your own design, or might include fancy scallops and designs for no good reason other than aesthetics.

Use your preferred cutting implement to cut the fender out of the plastic.