I pulled out the nail, got out my patch kit (bought a few days earlier at a bicycle shop), found the hole in the tube, patched it and was on my way. A few hours later, just out of Coco's corner, that squishy sensation came back. This time I didn't need the lady to tell me I was suffering from pneumatic dysfunction. I pulled out the tube and saw the now shriveled-up patch I had put on earlier in San Felipe.
She looked my way, smiled and said, "I think you're going soft."
Out of sixteen riders who made it to Mulege and back that year, only four were flat-free, seven had one flat, the remaining five averaged three flats each, and the record was four. Let's take the record holder -- me. How did I get four flats? Cactus needles? Hitting rocks at sixty? Nails? A cheap tube? Actually, I picked up one nail and then spent the rest of the ride fixing the same puncture over and over again. Other riders with more than one flat also had the same problem -- the patch failed. Those who took their tubes to a Llantera (a Mexican tire-repair establishment identified by half-buried old tire out front), however, had better luck. What do these statistics tell? They say that patching a tube may be trickier than you think, and learning how to do it right could save you a lot of time and trouble. To discover the secret, I watched what they did in the Llanteras, visited a couple of truck tire repair shops in Berkeley afterward, and talked with a salesman for tire repair equipment. I got pretty much the same story everywhere. First, you gotta have...
The Right Stuff
The thin patches used for bicycle tubes will disintegrate under the flexing and heat generated in a rear tire, as I discovered that morning in Baja. A knife, a rasp, and a piece of sharp, medium-to-coarse grit sandpaper will rough up the surface of the rubber and clean it. You'll need a stitcher -- a little roller-wheel with a serrated edge and a disposable acid brush -- to spread the glue. Finally, you need good glue and good patches. Most of the time, any tire-repair glue (cold vulcanizing fluid, or self-vulcanizing cement are the technical names) will work with any patch, but the technical people say there are some minor differences to be aware of. To avoid potential mismatches, get the glue and the patches from the same manufacturer, or use a combination that a tire repair shop will vouch for. The glue must be in a metal tube or container. Once a tube has been opened the glue will, over time, magically disappear. So have at least one unopened tube of glue with you, wrapped in duct tape to prevent it from flexing or cracking.
For a simple puncture, the patch should be about an inch and a half to two inches in diameter and about as thick as the tube. It will have a protective transparent plastic film on the front side and a feathered or tapered edge at the circumference. The patch should be intended for a truck-tire inner tube, not for a bicycle tube. The thin patches used for bicycle tubes will disintegrate under the flexing and heat generated in a rear tire, as I discovered that morning in Baja.
The hardest item to find is the stitcher. If you can't locate one anywhere, get a little plastic wheel, like from a caster or shelf roller. (That's what the LLantera in San Ignacio used.) I got a combination stitcher and rasp at the local branch of Myers Tire Supply in Oakland, CA. Myers carries a line of products from The Patch Rubber Company -- glue, patches, tools -- and distributes to tire stores. They were friendly and generous in sharing their expertise.
The patch should be intended for a truck-tire inner tube, not for a bicycle tube.
To be sure that you've got the right stuff, take an old tube and practice the techni'ues described below for roughing the tube, applying the glue, and stitching the patch. If you can't peel off the patch after it has cured for a half hour, you're in good shape.
Getting to work
You've thoughtfully brought with you all the tools needed to pull the wheel and tire; you have the tube out and have found a shady spot to perform the following operations with military precision.
1. Prepare the surface. The purpose of roughing up the surface of the tube is to expose fresh, clean rubber for the glue and patch to adhere to. The danger is always that you will not rough and buff the surface enough, rather than too much. Use a knife to scrape the surface first, then a rasp (like you get in a tire patch kit) to grind away the surface rubber, and finally the sand paper. The roughened area should be about a half an inch larger than the patch, all around. When finished, use the knife again and a puff of air from your lungs to get all the loose rubber bits off. You should not be able to recognize any vestige of the surrounding tube surface (pattern or markings) in the area you roughened. Don't touch the fresh surface.
2. Apply a thin, even layer of glue. This is best done with the acid brush, although a latex glove (unpowdered) will also work. If you don't have a brush or latex glove, place the opening of the glue tube directly on the inner tube and s'ueeze the tube gently as you move it in ever-wider circles. The point is to avoid using your bare finger to spread the glue, as the oil and grime on your skin is bad for the bond chemistry. Use enough glue to cover the entire buffed surface with a consistent layer that is minimal but with no bare spots. If the application seems too thick in some places and has already started to dry, proceed anyway.
3. Wait for the glue to dry so it's bone dry; not tacky, and certainly not wet. This can take anywhere from three to ten minutes, depending on the thickness of the glue layer and the temperature. If the application was uneven, just be sure to wait long enough so that the thicker areas of glue are completely dry.
Your mantra: "I will not touch the glue, I will not ...."
4. When the glue is dry, peel back a portion of the protective cover from the adhesive side of the patch. As you've already realized, you want to keep your fingers away from the adhesive surface of the patch. Use the portion of the cover still connected to the patch to grip the patch as you position it over the puncture and then set it down onto the tube. Try to have the first contact between patch and tube be at the center of the patch and then have the contact point move continuously toward the outer edges. This will prevent air bubbles and help ensure a smooth, uninterrupted contact between patch and tube.
5. Immediately place the patched area on a hard, smooth surface (gas tank, fender, or such) and begin with the stitcher, rolling back and forth vigorously, first at the center of the patch and then working out toward the edges. The stitching process is important because it initiates the chemical and mechanical bonding processes. This is also your last chance to get rid of any air trapped between patch and tube. Stitch in all directions. Press hard, as hard as you can. Remove any plastic film from the outside of the patch, and you're ready to install the tube and finish the rest of the job. Be sure to run your hand (carefully) around the inside of the tire to make sure that whatever caused the flat is gone and there isn't anything else present that could cause another flat.
Repairing a tire
If the tire itself is damaged (a cut or tear) such that it could damage the patched tube, then you will need to repair the tire as well. The patch to be used for this is different (larger, thicker, stronger, and less flexible) than a tube patch. The procedure for patching the tire is the same, except now you're working inside the tire, on a concave surface, and it will be much harder to roughen the surface properly. The Myers stitcher has a curved rasp that can be used for this. It's easy to carry along a few tire patches in your patch kit.
As long as you've got a tube in a tire, you can count on having the opportunity to patch it, sooner or later. Doesn't matter whether you're riding on dirt or pavement, it will come your way. Plan ahead -- have the right stuff with you when you need it.