Light Weight Coroplast Wheel Disc Are Cool!
OK! So now you have had a chance to make a fairing, or maybe even a tailbox. Wasn’t too bad at all was it? The first time is always the hardest, because you don’t know what to expect. Some things are easier than others, and then sometimes it just seems that way.
Coroplast can be used for so many different things, that it just takes patience sometimes and that “out of the box” thinking to do it. Anytime you start bending something that has a flat surface, you can bet it might bend one way, but generally it won’t bend in two opposite directions without creating some interesting and undesirable additional bends.
Wheel discs, which would seem simple enough to make at first look, can be a little more of a challenge than you might think. Since weight is always a consideration 2mm Coroplast is recommended.
It is also easier to bend into a cone, which you will be using for the dish on the spokes. Also, the 4mm has too much of an overlap from where it butts up against the spokes and the edge of the rim.
What you end up with is another place for the air to create drag, which is what you are trying to reduce in the first place.
Measure the inside of your rim using a tape measure. Stretch it accross the spokes, and make sure you run it accross the axel bolt. Let’s say that on a 700c wheel the measurement was 24″. Great!
Now get a piece of string, kite string or whatever and make a loop with a know in one end so it won’t slip. On your Coroplast, measure 25″, and mark the center at 12 1/2″. Take a nail, or any pointed object, place it through the loop and in the center you just marked on the Coroplast.
Stretch out the string to the outer mark. Now take a Sharpie and wrap the string around it at least twice, making sure you keep it on the mark. Tie the string in some fashion so it won’t slip. Holding the one end in the center, begin tracing the circumference of the wheels inside demminsion. When you are finished, cut out this circle. Next, cut out a 1″ circle where the axel bolt will go.
Find a point on the inner circle for the axel where the flute of the Coroplast runs straight from the center circle to the outer edge of the disc. Take your utility knife and cut this, making a slit.
Now overlap the two edges approximately 1 ” and use a piece of Duck tape to hold it in place. Center the disc on the wheel, making absolutely certain the center hole is centered on the axel.
Tape the disc to the wheel on the dished side, or opposite to the cassette. Take your Sharpie and from the cassette side begin marking where the edge of the rim and the Coroplast should be.
Once you have done this, take the disc and trim the edge to the TOP of the mark. It’s really important that you do not cut below the mark, because you will be cutting away more of the Coroplast than you need to.
After you have trimmed, center the disc again and see if the edges will go inside the rim. Re-trim as needed.
A tip when cutting Coroplast, is to make sure you have something with a straight metal edge to run your utility knife along. When you are cutting accross the flutes of the Coroplast the cut will be very jagged and anything but straight, unless you have something to guide the cut.
A wooden ruler will work up to a point, but eventually you will get the blade to dig into the edge of the ruler and the fun begins!
Remember, it’s always easier to cut more off, than it is to cut too much off! Many others have said it before me…”Measure twice, cut once.” I can say “amen” to that!
Once you have trimmed, go back and cut the overlap off the slit you made. Join the edges and use a couple of pieces of tape to just temporailly hold the two outer edges together. I use a simple transparent packing tape to hold the two edges together. Recheck the fit on the wheel to make certain it still fits the way you want before you go ahead.
Then on the inside of the disc, take a longer piece of packing tape, overlapping the axel hole, and take it all the way past the outer edge of the disc by about 2 “. Make sure to make as smooth a bond as possible, pressing out all the air and getting all the tape to stick to the Coroplast surface. Try to avoid wrinkles.
Slit the overlapped pieces of tape so that when you fold them over the edges they won’t wrinkle. Do this at the axel hole and the outer edge. Now take off the pieces used to join the edges on the reverse side of the disc and repeat the process.
Now, place the disc on the wheel. Find the air valve. Turn the slit so that it is at a 45 degree angle from the valve. In otherwords, if the valve is at 12 o’clock the slit would be at 3 o’clock.
Use your Sharpie to mark the position of the valve on the disc. Think about the nozzle on your air pump and how large it is. Consider how large an opening will need to be to get it over the valve once the disc is in place. Leaving a space of about 3/4 ” at the outer edge, measure 1″ accross and 3″ high (depending on the size of your pumps nozzle) putting the valve location in the center of this rectangle.
Now, consider which way the disc will be turning. Focus on the edge that will meet the air as that disc turns. This is the edge you DO NOT want to cut all the way through.
On the side of the disc that will be against the spokes, cut just the surface of the Coroplast for the edge of this door. This will act like a hinge.
The other three edges you will cut all the way through. If you do this correctly, you will have easy access to put air in your tire without having to remove the disc.The little door you just made can be taped shut with the same transparent packing tape.
Now you’re ready to attach the disc to the wheel. Place the valve door in it’s position and locate the spoke closest to the valve door. Remember the spokes will alternate, and you want to use just the ones that are on the same side of the rim as the disc.
Take a punch or sharp, pointed object, and punch a hole on each side of the spoke in the Coroplast. Use a Ziptie to secure it to the spoke, leaving the connection on the INSIDE of the disc.
Do not tighten the Ziptie too much to avoid crimping the smooth surface of the disc. Using the valve door as 6 o’clock, put additional ties at 9 o’clock, 12 o’clock and 3 o’clock positions.
Now check to see how well the edge stays against the spokes. If there are points where the edge of the disc wants to pucker out past the edge of the rim, use a Ziptie to even it up, even if it means using a spoke from the opposite side to do so. Just make certain not to pull it too tight and create the opposite effect.
One more tip. On the transmission side of the rear wheel, there is very little dish on an 8 or 9 speed bike, and you will be cutting a larger hole for the cassette. Just remember, measure twice, cut once, and you’ll be fine.
As always, the first one will be the hardest, but the benefit usually outweights the effort. I have some I have used for over a year. They are easy to clean and they don’t tear up easily.
Using these on the front wheel of a LWB is of questionable benefit. The steering can become “twichy” because the front wheel being lightly loaded will be catching cross wind that it never did before.
If it’s all about looks then it won’t matter. If it’s about speed, my best guess is 1/2 mph more with one on the front.