Making wheel disks for bicycles
How to Make Wheel Disks
Fiberglass disks ABS plastic disks Fabric disks  ZoteFoam disks
Wheels disks are like fairings for your wheels. They help guide the air around the rim, spokes and hub so that those components do not disturb the airflow. You can buy wheel disks for a variety of wheel sizes, but they are fairly expensive - about $60 per wheel. On this page you will find many methods of building inexpensive wheel disks, one by making a mold, then creating fiberglass disks, one using plastic sheets to make a "solid" wheel disk, and then another using nylon fabric to make a "flexible" fabric wheel disk. 

Building instructions for making a solid wheel disk made from Fiberglass:

By Warren Beauchamp
After trying a couple different techniques for making wheel disks, and not being too satisfied with the results, I have settled on the method outlined below to create tough and extremely aero wheel disks. 

Materials:

  • 1/4" foam insulation sheeting, available at your builders supply store. 
  • 3M Super 78 spray adhesive
  • Mold release agent (Available from Wicks Aircraft)
  • Fiberglass cloth
  • Epoxy or polyester resin. I recommend epoxy as it is less toxic and stronger.
  • Large compass (Home Depot) , small compass
  • Tape rule

This method involves first creating molds for the disks, and then laying up the disks themselves, trimming them, sanding and finished, and then attaching the disks to the wheels with wire ties at the hubs. Note that you will need to make 1 mold for each different rim dish. On most bikes this means 3 separate molds. Yee Ha...

The molds are made from 1/4" foam (usually pink and accordion folded), which can be easily obtained from your local Home Depot, or other builders supply store. If the foam has a plastic coating, you will want to peel it off, as it it harder to bend with the plastic intact. The two measurements that you will need to make are the disk diameter, which is usually measured to the inside of the brake surface, and the disk dish height. The disk height is the distance between the highest part of the hub (usually the spokes), and the part of the rim just inside the brake surface. You will want the disks to be as flush to the brake surface as possible for maximum aerodynamic effect. 

 

After you have measured the disk diameter, divide it in two, set your big compass to that distance, draw the circle on the foam, and cut it out. Here's where things get tricky. You'll need to cut out a pie shaped section by drawing lines from the center of the disk out to the edge, so that when the edges are pulled together, the dish height matches that of your rim. This may take a little trial and error, but fortunately, foam is cheap. 
You will also want to cut a circle out of the center of the foam disk that is the same diameter as your hub. This may require the use of a smaller compass. This will help the foam obtain to a nice cone shape form. Once you have cut your pie shaped section to the right size, you need to join the seam. 3M Super 78 spray adhesive is designed to adhere to this type of foam, and is quick and easy. Cut small tabs of foam to back the seam and attach with Super 78. This will ensure you have a consistent cone shape. Some duct tape also helps to hold things together while the adhesive dries. You'll also want to cut a long strip to be attached to the rim of the cone shaped disk. This strip provides rigidity and keep the cone from warping. Paint on 3 or 4 layers of mold release agent. The picture below shows the top and bottom sides of the mold, after the mold release agent has been applied.

Once the release agent has dried, you can lay in your fiberglass sheet, and paint on the epoxy. I use two layers of fiberglass, and apply epoxy then squeegee the excess after each layer.

Here in Chicago, garage temperatures rarely make it above 50 degrees F in the winter, so some type of oven is needed to ensure proper curing. Here's one of the disks cooking in my makeshift oven:

 

Once the epoxy has cured, the fiberglass disks should peel out of the molds relatively easily. This means the molds can be re-used.
Sand the mold joint ridge and any other imperfections off the disk with coarse sandpaper. Trim the disks to the correct diameter using your handy dandy compass. Using the smaller compass mark the inside hole, which should be slightly larger than your hub diameter. I needed to make my holes bigger on the front disk as I messed up my dish distance.
Finish and paint the disks. To attach them, you can drill a series of 1/8" holes in the fiberglass disk at the diameter of the first spoke crossing, leaving about 1/2" between holes. Plastic wire ties can then be uses to attach the disk to the spokes. This method of attachment also should pull the disks firmly against the rim of the wheel. You can attach the wire ties from the inside of the disk on one side for a cleaner finish. Or you can try an alternate method of wheel disk attachment.
Note that you will probably need to cut a hole in your wheel disk for tire pump access. You can cover the hole with some matching duct tape or packing tape to keep it aero. Also you'll find that the speedometer magnet on your spokes doesn't work so well now. You can tape or epoxy a magnet to the inside of the disk to fix this problem. I used the small rare earth magnets from my old SonicCare electric toothbrush head. Here's a picture of the Barracuda low racer with the completed wheel disks. 

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Building instructions for a solid wheel disk made from ABS plastic sheeting

By Warren Beauchamp

Materials:

  • Typically 0.035" (35 mil) ABS plastic sheeting is used because it is relatively lightweight, relatively strong, and it is very cheap. It is available at most plastic supply dealers in 4x8 foot sheets.
  • Aluminum sheeting, also about 0.035 inches in thickness. You can find this stuff in hardware stores, I used some intended for roof flashing.
  • Self adhesive 3/4" Velcro strips. I guess there are two kinds of this self adhesive Velcro. The kind you find in the hardware store, and some industrial strength adhesive stuff. Get the industrial strength if you can, I use the cheap stuff, but it tends to loose it's stick in the heat.
  • Clear plastic packing tape.
  • A large compass. I found mine at Home Depot.
1) Measure the inside diameter of your wheel. Add 1/8" to that measurement.
2) Use your compass to draw a 2 circles that size on your plastic sheet.
3) Draw smaller circles to mark where your hubs will be. If you are doing a rear wheel, you will have to draw a circle of the same diameter as the largest cog on your rear cluster on one on the sides. 
4) Carefully cut out the wheel disks, cut a slit from the outside to the center, cut out the hub hole.
disk1.gif (2194 bytes)

5) Place the wheel disk on the wheel. Notice that you will need to overlap the edges of the slit to make it fit your wheel's dishing.
6) Mark the overlap, and note any trimming that needs to be done to make the disk fit properly. The edge of the disk should line up with the edge of the rim.
7) After trimming (if needed), use the packing tape on both sides of the dished wheel disk to tape the edges of the overlapped slit together.

Pictured: overlapped slit

 

disk2.gif (2327 bytes)
8) Paint the disk the color of your choice.
9) Make 1" x 1" clips out of the sheet aluminum. These will fit on the spokes.
disk3.gif (1146 bytes)
10) Make enough for every other spoke.
11) Bend the center tab of the clip to fit around a spoke.
12) Mount clips on the spokes, push them as far as they will go over the spoke nipples.
13) Cut out squares of Velcro, stick them on the clips. Put the mating variety of Velcro on the wheel disk in the proper locations. You may need to stack up some Velcro to make the edge of the wheel disk line up with the edge of the wheel.
disk4.gif (1561 bytes)
Example wheel disk showing taped-over slit (yes, it's not very noticeable): diskex1.jpg (5103 bytes)
Example of clips and Velcro inside the wheeldisk assembly: diskex2.jpg (6091 bytes)

Alternate method of attaching solid wheel disks:
Don Smith describes this alternate (and better) method of attaching solid wheel disks.  

The things you need are Christmas light clips that are made by the Velcro company, and no the discs are "not" attached with Velcro. These clips seem to be made of about .090 Lexan. The flat bottom of the clips have Velcro on them....ignore it. These clips are shaped perfectly for their new intended use. The next item are these things called "pony elastics". They look like little black "bungee cords" and they're used for pony tails. The last item you need is some stuff called "Automotive Goop". There are several different kinds, such as "Household Goop", "Plumbers Goop", "Marine Goop" etc. They will all probably work, but I use the "Automotive Goop". Shoe Goo is probably the same thing. I tried several different things and this is the only stuff that works. I get all these items at the local Meijer Thrifty Acres store. Before I forget, the pony elastics come in different sizes...you need the size that looks like it will just fit over your thumb. They`re made by a company called Goody, and you get 30 for 97 cents. The clips are 20 for about $2.47 

Anyway, I lay the disc on the wheel in the proper position and use masking tape to hold there. Then I flip the wheel over and I take the Goop and glue clips between the spokes while paying attention which way the clip is facing in relation to the spokes on the opposite side of the wheel. Also, as an example, I use 4 clips on a 16" wheel, and 8 clips on a 20" wheel. 

About these clips...the flat side of the clip has Velcro on it. Leave it on, it let`s the Goop hold it better. One thing I forgot to mention, is that I scuff up the disc wherever I`m going to attach a clip so the Goop gets a better grip. 

After all the clips are good and secure, I take one of the little "bungees" and wrap it around a spoke and loop it back through itself...on the opposite side of the wheel from a clip, and then attach it to the clip. A little tip beforehand, when your installing the clips, is to pay attention to which spoke you will be attaching the "bungee" to, so that you can orient the clip in the best position. After doing this, remove the disc and do the other side. When the other side is finished, leave it on and re-install the other side in the same position you took it off or the bungees may not be positioned correctly for their clips. 

The whole process is really very easy, and other than the time it takes for the Goop to cure, it might take about 5 minutes per side to mount the clips and the bungees. Also, one of the things I really like is that you don`t need an access hole for your valve stem. Just pull the disc away from the wheel in the area of the stem, reach in and if you need to, disconnect a bungee and you have plenty of room to air up your tire. 

 

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Building instructions for making flexible wheel disks:

 
Thanks to Dave Larrington for posting these instructions on the HPV mail list

Ingredients:

  • Cable clips
  • Rip-stop nylon
  • Fibreglass kite spar or aluminium rod
  • Metal or plastic tube
  • Bungie cord

1. Get a box of cable clips - the sort which are normally fitted with a small nail for disciplining cables to skirting boards or over doorframes, etc. They look kind of like this:

clip.gif (813 bytes)

I use the ones for 6mm diameter cables. Black clips look better than white ones. Remove the nails.

2. Make the mounting clips. On my rear wheel (ISO 540), I have one clip on every spoke, but on a smaller wheel you can get away with fewer - my front disk (ISO 369) has a clip on every other spoke.
Depending on how keen you are, there are two options:

EITHER: drill the nail hole out using a drill bit about the same size as a spoke nipple. I used a 4mm bit, though something a little smaller might have been better - 1/8" maybe. Then undo the spoke
nipple, slide the clip over the end of the spoke with the open end of the cable slot pointing towards the hub, do the spoke back up again and slide the clip up over the nipple. I recently built a new rear wheel, so this wasn't as much of a pain as it would have been with a fully-built one.

OR: drill the hole out as above, then cut one side of the hole with a sharp knife, so as to allow the clip to be clipped onto the spoke. Make sure you do this at the SIDE, rather than the back (opposite the cable slot), as a slit in the back renders the clip more likely to pull off. If you are drill-less, you can alternatively make the cut first, then use an old spoke nipple to ream the hole out. You will probably need to hold it with pliers and bash it with a hammer, so take care of fingers and thumbs! Whichever method you use, fit the clips onto the spokes, with the open end of the cable slot facing outwards and towards the hub, then slide up onto the nipple.

The above rigmarole can be avoided if you can lay hands on some pukka Uni-disk clips. These clip on in the same way, but Uni-disk have done all the hard work for you. I had some left over from one I bought from a sale bin some years back - the disc itself has long since disintegrated but the clips remain.

3. Take a length of kite-spar or aluminium rod (genuine Uni-disks use the latter), bend into a circle inside the clips and cut to length. Join the ends into a hoop by whatever means available - a short piece of metal or (preferably) plastic tubing will do the trick. Try not to use so fat a tube that it sticks out a long way past the edge of the rim, as this could interfere with the brakes. If you feel so
inclined, glue the ends of the spar/rod into the tube - this might prevent it from going "sprong" at an inopportune moment.

4. Draw a circle on the nylon - the diameter should be that of the wheel plus a bit more - say 10 cm greater than the inside of the wheel rim. Cut out the disc, and cut an appropriately sized hole in the centre for the hub. Our local kite shop sells rip-stop nylon sticky tape, which is useful for reinforcing the edges of the hole.

5. Make maybe eight short cuts (~3-4 cm) at the outside of the nylon circle, pointing towards the centre, at equal distances around the circumference. Fold over the fabric between each pair of cuts, and sew up, so that it forms a tunnel around that part of the disc. Repeat until you have a series of tunnels right around the disc.

6. Thread the bungie cord through the tunnels, and tie a great big humungous fat knot at each end, to stop it from slipping out again.

7. Thoroughly soak the whole thing in cold water - when it dries out it should tighten itself more, and should still remain reasonably taut in the rain. It probably won't, but that's the theory...

8. Place the fibreglass hoop on top of the nylon disc; pull the cord as tight as possible. Ensure your hub hole is in the middle... Tie the two ends of the cord together.

9. Clip into place on the wheel. You may need to persuade it under the last few clips with a screwdriver or somesuch. Repeat for the other side. Don't forget to remove the freewheel/cassette first!

<silly_hippy>
10. If you, your partner, or your best friend's dog have artistic tendencies, paint swirly psychedelic patterns on the finished item! The Vertigo Records logo circa 1971 is highly recommended.
</silly_hippy>

Have fun. Take care in crosswinds, especially if you use them on the front wheel. I disclaim all responsibility.

Dave Larrington
Editor - BHPC Newsletter

 

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