|Click HERE to go back to the main Projects page
Zote foam wheel discs (revised 8/03)
by John Tetz
This page details the construction of ultralight wheel discs using Plastazote foam ("Zote foam") and the methods developed by John Tetz. For source information on the foam material used and additional info on working with it, see the foamshell page. There are many ways to make wheel discs, out of all sorts of materials. The most complete collection of these alternate methods is found at the excellent WISIL site.
The discs shown here weigh 77 grams (1.7 oz.) and are for a 406 mm (20") wheel.
This section drawing shows how the disc system goes together. The discs on either side of the wheel are attached to each other with small sections of hook-and-loop (Velcro) between the spoke nipples. Edge stiffeners prevent waviness. The spacer blocks bring the hook-and-loop pieces in contact with each other. The disc material I recommend is 0.125" thick, or possibly 0.15" for large diameter wheels (although I have little experience with larger wheels). Choose an appropriate thickness for the stiffener and spacer blocks to fit the rim width. In my case, all the materials are 0.125" thick for a 23 mm wide rim.
This shows a 0.125” thick sheet of Zote foam taped to a front wheel, ready to be heated. Heating the foam stiffens it and forms it. Use either LD45 (wider color availability) or the slightly denser LD60. The LD60 surface, which refects tiny specks of light, looks good in the sun. Stretch the foam fairly tight with the tape by going around and around, pulling the tape at the tire a little tighter each time. Keep the hub hole centered during this process.
This shows heating the back side only, which seems to work better. Heating the front side causes the masking tape to come loose, resulting in uneven tension and waviness. Play the heat slowly from the outside edge to the middle as the wheel is rotating for at least two minutes. The wheel rotates by the force of the heat gun air. Leave the foam on the wheel and mark the area where the stiffener will go. Cut a small section of scrap stiffener, slip it behind the spokes, and draw in the stiffener area.
This shows applying contact cement to the back side of the disc. Applying cement to an unmounted disc causes the disc to warp, yet by leaving the disc under tension, it remains flat. After the contact cement has dried thoroughly, remove the disc.
This shows making stiffeners out of scrap materials. Measure the radius to the inside of the rim for the outer diameter of the spacer, and make the width about 1.25”. Use a radius stick (thin piece of wood) to lay out the cut lines. Match the ends by cutting at 45 degree angles to spread out the joint. Matching can be done by laying the stiffeners on the disc, drawing the 45 degree angles, and cutting them (off the disc). Wait to cut the very last match joint until the last section is glued to within 1” or so from the first section in order to make the final trim cut more accurately. I use HD80 material because it is much stiffer than the LD materials. For both materials (especially HD80), rough up the glue surface first with coarse sand paper, then apply a coat of cement and let it dry. Next, apply a second coat to both the stiffener and the disc, let them dry for a few minutes, and then press together.
This shows the stiffener glued to the disc. Note that the ripple on the outer edge of the disc is from the taped edges around the tire. The excess slightly beyond the stiffener will be trimmed off later.
Put the disc temporarily back on the wheel with a few pieces of masking tape. This photo shows marking the spoke and valve locations. This will give the location of the extra spacer blocks needed to bring the sides of the hook-and-loop in contact with each other. Leave a bit more room around the valve.
This shows the small blocks glued to the stiffener. The outside diameter has also been trimmed.
This shows the finished discs. Use hook-and-loop that has adhesive on the back side, as wet contact cement and hook-and-loop don’t mix well. Mark the valve location on the outside of the disc. To put air in the tire, simply pull the hook-and-loop apart for about ¼ of the disc.
How much aerodynamic improvement do the discs make? Not enough that I can tell by feel on a small wheel bike, but combined with other improvements, they add up. I do feel a little bit of front-end wander from cross winds, although not as much as in a streamliner. The discs do not slow acceleration because they are so light (and dead silent), and they do make this bike look sharp.
International Zote foam suppliers:
For a wider range of materials in the US, see: