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| How to make an Ice Tire |
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This winter I'm battling the elements on the East coast. I had forgotten what real winters were like. Now that I'm properly acclimatized to the sub zero temperatures, I've decided to take a short mid winter vacation and go further North. I'm visiting Montreal QC in a couple weeks to compete in one of their annual bike events, La Coupe Des Glaces.
Around Manhattan, I'm fine running my 23mm slicks at 30psi less than normal (thats down to 90 from 120) or taking my mountain bike over the frozen tundra if its too deep to be navigable on slicks. I'm generally not riding around on a sheet of ice in Manhattan though.
La Coupe Des Glace calls for something a little more hardcore. Here I'll show you how to make a dedicated ice tire (or two!)
Supplies needed:
- Older cyclocross, mtb, or path tire, depending on use
- #8 x 1/2" Lath screws or equivalent button head screws
- whiteout or chalk to mark the tire
- Screwdriver
- Scratch Awl
- Old tube
- Spray adhesive
- Disc grinder with cutoff wheel
- Safety glasses
Tire Selection
The reason I mention using a cyclocross or path tire is due to tread pattern. We want something with as much contact area as possible on the centre tread. This can mean a wide tire, or if your bicycle does not have room for wide tires, then something with knurling along the centre tread will work well. Another criteria is shoulder blocks. These are designed to dig into the earth during cornering in regular use, and we're going to use these to hold the screws.
After you've selected a suitable tire, fit it on your bike to see how much room you have. Depending on whether you are using it on the front or the back, check the fork clearance, or the chain/seat stay and bridge clearance. On my bike I am barely able to fit a 32mm cyclocross tire in the fork, so I've only got about 4mm to work with. This lets me know how aggressive I can make the tire.
Tread pattern planning
Depending on how much work you want to do, as well as how heavy you want to make the tire, you can decide upon the tread pattern. Look for thick shoulder blocks that you think will be suitable for holding a screw in place, and mark them with whiteout. Symmetry is helpful, as you want the bike to behave predictably turning both directions. When the bicycle is traveling in a straight line, you do not need all your weight to be traveling on spikes. Instead, think of them as lining the edge of the tire's contact patch. It is when you lean the bicycle that you really want the spikes to dig in. It is a good practice to add two levels of spikes to different angles of the tire's shoulder, this will avoid a sudden 'breakaway' if you lean the bicycle too far.
Screws
Figure out just how many screws you are going to need per tire. You don't want to run out halfway around the tire. For my Bontrager Jones CX tire I used 208 screws. I used lath screws, because they are like a button head with a built in washer, giving the head a very large surface area. This enables the tube to push on the screw with enough force so that it doesn't bend over, and tear the casing. This also helps with traction, keeping the spike digging into the surface of the ice.
Technique
Using the scratch awl, punch a hole into the tread block from the outside, ensuring that the awl goes through the casing far enough to leave a small hole in the casings threads. Now remove the awl and put the screw through from the inside, turning it until the screw head is seated against the inner casing. Do not continue to turn the screw after this point, because it will enlarge the hole and possibly damage the casing.
This whole process can take quite some time, so I recommend you start a movie, or queue up some cartoons in your media player's play list. A cup of coffee really helps at this point too. Here's what the tire will look like after this step:
Mounting the tire
In order to protect the tube from the screw heads, which will constantly shift under use, we need to add a second tube to the inside of the tire's casing. The easiest way to do this is to first cut the tube to the correct width, so that it covers all of the screw heads, but does not interfere with the tire's bead. Next use spray adhesive on the inside of the tire and the lining tube, so that it is held in place, centered in the casing. This makes the actual tube installation much easier. Next, mount the tire on the wheel as you normally would while changing a flat. Be careful though, those screws are sharp. I was able to inflate the tire to 100psi without any tube or casing failure. I won't run it at this pressure on ice, but its good to know that it will hold up.
Trimming the spikes
This is necessary for a couple of reasons. Currently the tire is quite dangerous, and hard to hold. Also, the spikes are too long to be practical. In use they will dig into the ice, but they will have a tenancy to fold over and scratch along the surface. This can lead to premature casing failure. Having them short and cylindrical in shape ensures that they dig in, without folding over.
With the tire inflated on the wheel, I found it easiest to mount the wheel on a fork that was clamped in a vise. If you do not have a vise, this step can be done seated with the tire on the ground held between your legs. (just be sure to wear thick jeans and maybe wrap the tire in a rag to avoid hurting yourself).
Once you have your safety glasses on, its time to get to work with the disc grinder. Cut each spike off to a uniform length, perpendicular to the screws orientation. This takes some time. Use quick passes from the side of the screw, instead of holding the grinder down on the screw tip and pushing. If you grind the screw for too long, it can heat up, melting the tire. On my tire I trimmed the inner screws down to 2mm from the tread block, and the outer screws to 4mm from the tread block.
That's it. The total time it takes to make one tire is approximately 3 hours, and the cost is less than $5.00 in screws. Now, I've just got to make a second one in time for the race and I'll be set.
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