Hey everyone! It’s Josh from Cry Baby Cycles, and we're taking on rear fenders for this tech article. One of the most frustrating things on a build is having a rear fender that just doesn't fit right! Either it's too big, too small, doesn't fit the radius of the tire well, or just plain looks stupid! This used to drive me crazy! So this is my step-by-step procedure to build a kick-ass rear fender for your build that fits the tire, bike, and your style perfectly to get that killer look!
Now, there are several ways to build fenders, but this is the way I like to build one piece fenders. I use an English Wheel, Planishing Hammer, Stinker/Stretcher, Bead Roller, a shot bag and mallet, and some pick and file tools. Rear fenders can be tough to make, time consuming, and sometimes take multiple attempts. There is a lot of shape to them and it can be tricky and frustrating! But once you figure it out it's a game changer on a build and can separate your build from the pack!
The first thing to do is always check your tire pressure and make sure its at its proper PSI. This is important because this can change the radius of the tire and you want it to be the right shape. Then I place a piece of welding rod over my tire to get the length of my fender. This will always vary depending on what you want the fender to look like. It's also important to have at least an extra 1" on each side so when you go to trim it, it's not too short. FYI always make things a little big when making parts!
Check to make sure your tire is straight and your chain is straight as well; so when you go to mount your fender its all properly inline together. If this isn't figured out your fender may rub.
Now I take another piece of welding rod and I bend it to figure out my length that I want for my radius of my fender, in this case I want it to be the same shape as my tire....once again leave some extra; we will be trimming it.
This is now my length and width of my fender:
I now stretch out my welding rod pieces and this will be my lengths I will use to build off of.
For normal, non-passenger rear fenders I use 18 gauge steel and for passenger fenders I recommend 16 gauge but it’s pretty tough to shape! Try not to use anything thinner than 18 gauge. Now I can lay my measurements out on my piece of steel.
Once I have cut my piece out, I’m ready to get the mallet and shot bag and start roughing it in.
I make a centerline and some cross lines so that when I’m roughing it in with the mallet I can hit it somewhat evenly. Then I wheel it in the English wheel. You don't have to use a mallet you can use the English Wheel the whole time to stretch the fender; the mallet work just makes the process faster.
I make the same line on top of my piece so that I have a reference of the center of the fender. I wheel the fender lengthwise and widthwise. This does three things; First, it smooths out the roughed-in hits. Second, it stretches the metal so that it will allow me to shrink the edges. Third, it pulls the fender around and starts getting my radius. When doing fenders, this is what makes it hard; you’re trying to make the diameter of your wheel and the radius at the same time! This is considered a compound curve.
Once I repeat the rough-in/wheeling procedure several times I start to get shape going on the fender. Then I start to shrink the edges as evenly as possible. This helps achieve the right radius of the diameter of my tire by shrinking the metal and pulling the fender around. Don't over-shrink or over-stretch the metal! Take your time and ease into the process! Remember: it's way better to be under-radius...once you go over it can be hard to take it out.
After repeating the process of using my mallet to get some shape faster, using the English Wheel to smooth out and stretch, and the shrinking to help pull the fender around it's starting to look like something!
At this point I'm about halfway there, and I continue to shape until I feel like it’s time to start checking fit on the tire.
I love the Planishing Hammer! if you don't have one you can use the wheel, mallet and bag. This once again helps the process go faster and I can get the sides a little easier. At this point, I jump on it and start planishing my radius out.
Now I start to slow down on shaping and start to check fitment often....remember you don't want to go over!
Now I'm really starting to get a nice shape of the radius of the tire as well. FYI to get to this point can take a long time so be patient it doesn't happen fast!
When I start to get really close I go back to the English Wheel only! No more planishing hammer and no more mallet. Now I'm trying to fine tune the fender and start to metal-finish it out. I'm using light pressure on the wheel as well so that I'm not putting wheel marks in it either.
Now after fine shaping the fender, I’m happy with the way it fits the tire diameter.
I’m also happy with the radius of the fender.
At this point I trim the fender to the desired shape that I want. I usually use green painters tape for this.
The ends of the fenders can get a little weird, and this is where the extra comes into place. As you can see I am now ready to cut the shape of my fender out.
Now I have a fully roughed-in fender!
The fender is hugging the tire nicely!
I take the fender now and put it on a flat table. I make sure that both sides of the fender are flat to the table. If it’s not quite there, you can use a hammer and dolly to straighten them out. This is important to do because against a straight tire, you will see waves!
Now we're ready to fine tune the fender and metal finish it out. I do this with a hammer and dolly, pick and file or bullseye pick, blueing dye, radius gauge and some sanding blocks. As you can see, I have sprayed the fender with the dye and then with go over it with the sanding blocks and file. This will show me the highs and lows of the metal. I then use the bullseye pick to pick up the lows and the hammer and dolly to smooth out and get the highs down. I use my radius gauge to make sure that the radius of the fender is the same throughout.
I start to sand the fender in all directions, then the blue that shows up is the lows.
If there are any really bad spots, I go to the wheel and wheel them out. You can also use the wheel to help get the metal finish process done, but very lightly because you don't want to change the shape of the fender, or leave wheel marks.
As you can see after two pick and file rounds, I have no blue dye showing and Im ready to DA my fender with 80 grit paper. Then I use a grey scotchbrite pad to finish it out.
We now have a fender!
This is what the fender should look like after a nice pick and file, DA sanding, and a scotchbrite treatment. A nice smooth-to-the-touch feel and an even-sanded look.
The next step is to gap your fender to the tire. I use builder magnets that are ½” in height. You can go lower to the tire, but with speed and heat tires will expand and everybody knows it sucks when tires rub or leave heat marks on fenders! I've seen so many problems over the years with fenders that are too close to tires and its sucks after all this hard work to remount or remake a fender; so be careful!
I set them in the front, rear, and center. You can use a number of things to gap a fender, rubber strips, chains, blocks..all kinds of stuff!
After I sit the fender on the tire and get it positioned, I pick a place off the tire and measure the sides so that they are perfect to the radius of the tire. You might have to do some detail trimming and sanding to make sure it's even all the way around.
The final step is to put a detail bead around the fender for strength and looks. On this one, I used ¼” tape to mark my bead layout. If you don't have a bead roller its no biggy I just like to do this.
I place the fender in the roller and do a test pass by hand to make sure the fender won't bind anywhere. 35. I match the tape with the bead I'm going to roll (which in this case is ¼”) and follow the tape line. If you’re going to do this be careful and TAKE YOUR TIME! You have one shot to do this and if the bead gets off your starting over on the fender!! This can be stressful after all the hard work making the fender! lol!
Now we're done!
A handcrafted, one-off fender that fits your tire, bike, and style!
Thanks for reading! Build & Destroy!