Fenders are nice to have when you need to ride in wet weather. Road gunk spraying you from below is a lot worse than rain pouring on you from above.
I wanted a fender for my 26" front wheel. Turns out a license plate works perfectly. It's the right length and width and can be bent to any shape. Plus it's highly reflective for night riding.
Unfortunately for us Yanks, U.S. license plates are too short and fat for the job, but European style plates seem to have the perfect dimensions (520mm x 110mm).
Luckily for me I had a souvenir plate from Germany that my sister gave me. I had no problem deeply offending her by destroying her gift. It says "BITBURG 05." Bitburg is a small German town whose claim to fame apparently is that Reagan caused some controversy by visiting in 1985.
If you are in Europe (or apparently certain former colonies), the first step will be easy for you. Go outside with a screwdriver and steal the license plate off the first car you see.*
I didn't need a rear fender because my rear rack already blocks any spray. You would probably need 1.5+ license plates to cover your rear tire.
* Disclaimer: don't do that!
Step 1: Materials
You will need:
-a long skinny European style license plate
-a piece of flat aluminum bar stock (I forget the exact dimensions but about 1/8" thick, 1/2" wide, and 30" long)
-2 u-bolts (the smallest size that will fit around the blades of your forks - mine had shocks and so may have been thicker than yours)
-shears that can cut through sheet metal
-a pop rivet gun and 1/8" rivets(or some small screws and nuts would work instead)
-pliers or a vice are useful for bending the metal
Step 2: Cut the Plate Into Segments
The more segments you create, the smoother the curve will be. I only gave mine 9 segments and it looks fine to me.
First use a ruler and pencil to draw on the back of your license plate and plan out all of the cuts and folds.
Each of my segments is about 2" long and is cut 1" in from each side, leaving the final width of the fender 2.5" (it was originally 4.5" wide).
This sizing has the bonus of keeping the plate legible, so people will know my love for Bitburg everywhere I go.
Don't forget to leave the appropriate length on one end so that it can fold up and be screwed into your fork crown! The sides of this uppermost section will be removed completely, rather than just folded down.
When you've got it all planned out start snipping with the shears - nine evenly spaced 1" cuts on each side.
Step 3: Bend Into Shape
When all the folds are there it is a matter of fine tuning each one so that it forms a smooth curve that matches the shape of your wheel. The best way to do this is fit it over your tire. The side flaps will overlap each other a bit.
Some advice: I cut the flaps of each segment and folded them down to make the "sidewall" before curving the fender into a circular shape. It would have been wiser to first shape it into a semicircle and then bend down the walls. Because of this my fender has a slightly irregular shape. Learn from my mistake -- form the flat license plate around a bike tire first, and then fold down the walls.
The first segment in the front of the fender should be bent up at a 90 degree angle from the wheel. This piece will screw into the fork. I trimmed off the sides of this segment because no sidewall is needed here.
Step 4: Attach Top to Fork
Actually in my case it guess it is called the fork brace because I have a suspension fork.
But either way you will need something to screw into. At the center of my fork brace there are two threaded holes that accept the same screws used for your water bottle holder. I think most regular bike forks have a single threaded hole in the crown that takes a larger screw. You'll need to find one the right size.
Find the proper spot to drill a hole(s) in your fender. This will determine the distance between your fender and tire. I don't know how close it should be to the tire. Half an inch or so?
Drill the holes and screw it onto your fork. I folded the top over my fork brace.
Step 5: Create Arms
Cut the arms down to an equal and appropriate length with a hacksaw. It will depend on where they attach to the fork. I'll get to that in the next step.
Rivet the arm to the fender. First drill holes through both and use a pop rivet gun to put 1/8" rivets through. If you cant get a rivet gun maybe you could use short machine screws and nuts.
As you can see in the pictures, originally I was going to connect the aluminum bar to the underside. But then I realized it would be better to rivet it to the walls of the fender so that the arms can rotate where you need them without changing the shape of the fender. So I drilled out the old rivets and put new ones in the sides.
Step 6: Attach Bottom to Fork Blades
However my bike had no eyelets and I decided to use a U-bolt on each side to grip the fork blades and hold the fender stays. I got the smallest U-bolts that fit around my fork, which is fat because of the shocks.
Drill a hole in the end of each aluminum arm so that it it can be tightened on to the U-bolt. I had to use a bunch of washers on mine as spacers because the bolts' threading stopped too short to be completely tightened.
The bolts are long and will protrude out. Chop off the excess with a hacksaw. Or maybe sharpen them into Ben-Hur-style anti-pedestrian blades if you are evil.
Actually, now that I think about it, you could attach all kinds of ridiculous stuff to the U-bolts: a front rack, a lance, a biking umbrella, or maybe a pair of sawed-off shotguns with handlebar triggers (if you happen to bike in a post-apocalyptic war zone).