Introduction: DIY Bike Fenders

For the most part, I enjoy fiddling with bikes more than riding them.  I'm really a big baby and I hate riding up hills.  That being said, a bike is a great thing to have when you need to get across campus.  I recently bought a 20" folding bike and it's a great little bike, but it didn't come with fenders.  What did you expect for $330 shipped?  I put up with the mud spray for a month but enough was enough and I decided i needed to fix the problem.

So off to my local bike shop and sticker shock!  $44 for a bit of plastic and some mounting hardware!  I knew I could beat that AND have make it look better.  Good thing I planned for this occurrence in advance.  So off to Ace hardware across the street and 4 minutes later, I have a spool of 14 guage steel wire and a .125"x1.5"x4' strip of aluminium stock.  I already had the mounting hardware I needed.  Total cost?  $13

I made the fenders and didn't document the process, so I'll walk you through with the pictures I have and draw the rest.  

I'll walk you through the process of making the rear fenders and then give a guide on how to do the front ones.

Let's get started!

Step 1: What You Need...

Now, I labeled the list required and optional, but you really don't need most of it.  Remember, this is instructables.  If you're feeling ghetto skip to step 10

3x M5 machine screws (can be socket, phillips, flat, torx, w/e you can find and have a driver for)*
6x Washers (or more)
1x Aluminium flat stock (3mm/.125" thick)**
1x Spool of 12 or 14 guage steel wire***

A drill
A hand saw or band saw
Flat file (you can use any kind you want, but flat is easiest)
Wire snip
Drill bits (1/4" & 3/32")

Sand paper (120grit)
Masking tape
Steel wool
Center punch (a wood screw will do)

Some puddles to test your shiny new fenders on!

* Depending on your bike, you may have trouble with really long screws.  I would suggest something between12mm and 16mm or you may run into your hub or kickstand mounts.
** Depending on your wheel size, you may need more than 1 piece of aluminium stock.  My wheels are 20" so I only needed one 4' piece for both wheels.
*** how much you need depends on your wheel size, but a good rule of thumb is the radius of your wheels times 5.

Step 2: Designing the Fenders

I did a bit of research, read google images, on fender design.  Most, if not all retail and custom jobbies have really complicated mounting hardware that's riveted or bolted into the fender.  Too much work.

I decided on this design.  The wire braces will thread through two holes from the inside and wrap around the top edges of the fender.   Then the braces are bent into loops at the bottom and screwed into the frame with the M5 screws.
Another M5 screw goes through a 1/4" hole on the fender and is secured to the bike.  

No complicated hardware here.

I used a simple compounded curve, but you can make them fit your style.  You could try an octagon or some ofther faceted style instead of a smooth curve.

Keep in mind most bike wheels (if not all) are round.  So fenders that fit around a wheel will most likely have a similar shape.  

Step 3: Cut the Metal

The stock I found was the perfect width for my tires, your mileage may vary.  If they are too wide for your tires but fit within your brakes, I would leave it alone.  If they interfere with your brakes on the other hand, you'll need to cut them down to size.  Try taking a chunk out of each side with a file.

So now that they are the right width, you'll need to cut them down the the right length.  I made a paper template from some 80lb art sketch paper but even newspaper would do the trick.

I taped the paper template to where I wanted it on the lowermost fender mount and then bent it around the wheel until I found a length I liked and then cut off the excess.  You can do this with the wheel off, but I think it's easier to tell if the curve works if the wheel is still there.  When designing the curvature, you want to make sure there is a good inch or more of clearance between the fender and the tire.  Accidents happen and getting your fender crumpled in the rear brake could get ugly.  Make a mark on the paper where the bottom mounting hole is.  I used a pushpin to poke a few holes so I was sure I got the right spot.  Don't worry if it is off center, we just want the distance from the end of the fender.  One hint I have is to let the lowermost end of the fender go past the bottom mount so you protect the bottom bracket a little more.

For 20" wheels, I used about 30" for the rear and the rest is enough for a small front fender.

Once you have your length, put some masking tape around where you are cutting to keep the edges clean and use a hacksaw or band saw to make the cut.  

Disclaimer: Don't use tools you feel unsafe or uncomfortable with.  I cannot be held liable for injuries to your person due to user error.  

Step 4: Drilling the Mounting Holes

Once you have the piece of aluminium the right length, we need to drill out where the bolts and wire-braces will mount.  Take your paper template and lay it on top of the metal.  Starting with the bottom hole, using the distance you marked in step 3 (with a pushpin) mark a point in the center of the width that distance from the bottom where the hole to mount the fender to the bottom bracket will be.  Put some masking tape over the mark to protect the metal.  Take your center punch or a wood screw and hit it with a hammer so you make a little indentation in the metal where you want the hole.  The aluminium is very soft, so just about anything will do as long as it is steel and pointy.  Maybe the same pushpin you used to mark the hole?  

Now we need to make the brace "mounts"
From the other end of the metal piece, measure up 2-3 inches from the bottom and make a line perpendicular the the sides.  Measure about 1/4"/1cm from the outside edges on the line for both sides.  Mask with tape and mark both holes with a center punch/screw.

Repeat this 8-12 inches up on the strip so you have a total of 5 center punched marks.

Get out the drill and go to town.  

The brace mounts (x4) will need the 3/32 bit and the M5 screw hole (x1) needs the 1/4".

Step 5: Filing for Safety

Now that you have your wonderful rear fender all drilled and cut, we need to clean it up.

Remove the masking tape.  Take the flat file and first round off the edges.  The last thing you need is to slice your leg open on your brand new fenders.  I mean, think of the mess and how much blood you'll need to clean off your bike.

I decided to do all 4 corners and round it out just enough so it looks nice.  Feel free to let your inner artist out now and do whatever you want.  You could make some intricate end flourishes or some kind of motif or even an animal head.  Just make sure to get rid of all the sharp parts and burrs.

Then clean up the drill holes.  You may end up marking the surface near the edges with the file, but we'll sand that away later.  Same as before, just clean up the burrs so you don't snag your fingers on it or make a run in your stockings. 

Step 6: Bending

Use your hands to rough out the basic bend.  This may take some trial and error.  Don't be afraid to unbend something if it doesn't look good.  I went for a smooth continuous curve for the main part of the fender, but this is your fender, personalize it if you want.
Just don't forget that you want the free end curved away from the wheel or something may push it into the spinning wheel where it'll get jammed or worse.

You may need to use pliers to get the free end to curve out a little in the 2-3" of space below the first pair of brace mount holes you made.

Once you're satisfied with the may the curve looks, try it on the bike and see if you have the 1-2" of clearance you need and that the free end is curved up enough so the lip can't catch on the wheel, even if it gets squished.

Step 7: Sanding and Polishing

Now get out the sandpaper (if you want to) and get rid of any scuff marks or machining blemishes in the metal.  This is a purely aesthetic step, so take as little or as much time as you want.

Follow this up with higher grit sandpaper or my personal favorite, steel wool.  Start with some really coarse stuff and work your way up to 0000.  Stop whenever you are happy with how shiny it looks.  I'm partial to the brushed look, so I stopped after the coarsest grade.
Again, this is for vanity (and pride) so work until you are happy with it.

You can even try for a polish if you want to spend the time.

Step 8: Mount It.

Remove the rear wheel of your bike.  It'll be mostly impossible to put the fenders on with the wheel still there.  If you are having trouble, try looking up a guide on google or watch this convenient youtube video...

Now use the M5 screw and washers to attach the fender to the bike.  I didn't want to scratch the paint on my bike, so I put 1 washer between the bike and the fender, and then one more between the fender and the screw.  Tighten it just enough so it stays put.

You may find it easier to turn the bike over on the seat and handlebars at this point.

Now take the wire and cut 2 pieces, each 2.5 times the radius of your bike wheel.  Gently bend it so it looks like a staple with really long prongs.  You want the flat part to be the same width as between the holes you drilled.

Thread the wire up through the holes from the inside, so the long legs stick out.  Bend them over the edges so they point back to the dropouts and the mounting holes.

Tighten up the M5 screw and reattach the wheel.

Straighten out the brace wires to where they will attach to the bike.  This will make them stronger and look better than if they have kinks.  Center the fender over the wheel.  Determine how long you need the braces to be on each side and cut the excess wire about 1" below that.

Take your pliers and curve the ends of the wire around in a loop big enough for a M5 screw.  If it is a bit long, you can double the loop back on itself or re-bend the wire loop and cut off the excess.  Do this for all 4 braces.  Take the rest of your M5 screws and washers.  I wanted to protect the paint job, so I sandwiched the loops between the washers before putting the screw on.

Step 9: Final Check and Front Fenders

Make sure everything on the bike is tightened up and flip the bike back onto the wheels.  Push on the fender a little to see it they hit the wheel.  If they do, try using a bit more wire or undoing some of the loops at the end.

If the curve isn't what you want, you may need to remove the wheel and fender and re-curve it.  Trying to re-bend it while the fender is attached may not work too well because you need to bend metal past the deformation point before it holds a bend.

Once everything is how you want it, pat yourself on the back, you just made yourself a shiny new rear fender.

To make a front fender, make another paper template, or eyeball it.  Cut the length you need or use the scrap from the rear wheel.

For the front, we only need one set of brace wires in the back, but need the front lip bent up with a hole for a bolt.  Do the same steps for machining the aluminium and making the braces.  Don't forget the curve on the free lip.

Step 10: Ghetto Alternatives

My favorite part, ghetto mods!

Now remember, just because you made it with ghetto means and materials doesn't mean it has to look ghetto!

No aluminium stock?  
That's okay, use some thick cardstock with a lot of duct tape.  You can even wrap it in foil to add bling.  Just use it the same way as the aluminium except for the filing and sanding/polishing.  Use can use scissors to round off the edges.  just remember to tape the corners again, or they won't be waterproof.
You could also try the plastic they put in chainlink fences or the time honored coroplast (election sign corrugated plastic).

Can't strip enough telephone poles for wire?
No problem!  Scrounge up some wire coat hangers and you have your braces.  If you're already appropriating some chain link fence plastic, why not take some of the fence too.  It works as wire in a pinch but you have to unwind it first.

Too cheap for screws and washers?
We can make it work.  For the braces, it's simple.  Take one of the braces and form it into a loop like in the instructable, but make it smaller.  Take the other brace on that side and thread it through the loop.  Take the non-looped wire and thread it through the fender screw hole on the bike.  For the bottom bracket part, take a spare bit of wire or a brad fastener and stick it through the hole.  viola, hardware-less fenders!

Too lazy?
Well, you're on the wrong site then buddy.  But maybe we can make something work for you.  leave a comment or PM and we'll see what kind of bike-store-markup price I can arrange for you.

Metal Challenge

Participated in the
Metal Challenge