Puncture vine (tribulus terrestris), also known as goat head thorns (The photo is from Google Images), is a big problem for bicyclists in several parts of the United States and also in a number of other parts of the world. It is certainly a problem in southwestern Idaho where I live. Even if there are no puncture vine plants in your immediate neighborhood, the thorns tend to blow into places where they did not grow. They have a knack for finding your bicycle tires. They are 100 percent effective at causing your tires to go flat.
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Step 1: Slime
I have decided a sealant additive is my best choice. I use Slime, which is a brand trademark. My bicycle tubes use Presta valves, which are thinner than the more common Shrader valves found also on all automobile tires. It is easy to remove the valve core from a Shrader valve, add Slime to the tube, and replace the valve core. Presta valves have their broadest part inside the stem so that it is impossible to remove the core from the tube.
Another Instructable slit the tube with a knife, inserted the Slime through the slit, and added a tire patch. The problem with that approach is that the least amount of Slime on the surface of the tube makes it impossible for a tire patch to stick. This Instructable will show you how to drop the valve core inside the tube and put it back in place after adding Slime to the tube. In the interest of disclosure, this basic procedure is described on the Slime website. I have illustrated it here with some things I learned by experience.
Slime coats the inside of your tire tube as your wheels roll. When there is a leak, the air moving through the leak draws some of the Slime into the hole and tiny shreds of rubber plug the hole. A tube with Slime added can last a very long time after a leak developed and sealed, even at pressures of 100 pounds per square inch.
Step 2: Remove the Nut
Use a pair of pliers to remove the nut from the thin threaded visible portion of the valve. The threads may have been crimped a little to prevent the nut coming off accidentally. Save the nut because you will be putting it back onto this thin stud.
Step 3: Drop the Valve Core Into the Tube
It sounds like the worst thing you could do, but allow the valve core to fall into the tube. Blow on the end of the valve stem a little to inflate the tube enough that the valve core can fall into the tube. If the valve core sticks in the valve stem, push the core out of the stem with a finish nail.
Step 4: Prepare to Pump in the Slime
Be sure to buy Slime designed for bicycles. The shreds of rubber suspended in the green solution are finer than those in Slime for automobile tires or for motorcycle tires. Slime comes with a clear plastic tube for connecting the bottle to the tire valve stem. It is sized for a Shrader valve. Use a brass Shrader to Presta converter. See the yellow text boxes.
Attach the clear plastic tube to the bottle of Slime. Screw the brass converter onto the stem of the Presta valve tire tube. Connect the clear plastic tube from the Slime bottle to the brass converter.
Step 5: How Much to Add
My tires are 700mm x 23mm. That is almost 27 inches in diameter and just under 1 inch in width. Four ounces of Slime is about right for my tires. The Slime bottle has markings in four ounce increments. Although difficult to see in the photo, you can see a slight difference in color that indicates where the level is inside the bottle. Squeeze the bottle to pump Slime into the tube. You may need to manipulate the tube to allow the Slime to pass beyond folds and crimps in the tube. You may also need to twist the bottle cap open half of a turn and allow air back into the bottle. When finished, remove the Slime bottle, the clear plastic tube, and the brass converter. Rinse the clear plastic tube so it is free of all Slime residue.
Step 6: Find the Valve Core
The valve core is easy to locate inside the tube. It has probably settled into the lowest part of the tube. Pinch along the length of the tube until you feel the valve core. You may be able to make it fall back toward the valve stem, but then you will need to locate it again. (Second photo) You will need to move it along part of the way "inch worm"-style. (Third photo) This means you pinch the tube against the end of the valve core more distant from the stem. Then pinch and push some of the tube in front of the other end of the valve and grasp the front end of the valve. Release the pinch at the rear. Pinch where the rear of the valve is now.
Step 7: Tip and Push the Valve Into Place
It sounds terribly difficult, but is actually quite easy to tip the thin end of the valve core into the valve stem. Then push it into the stem as far as you can.
Step 8: Put the Nut Back in Place
You will probably need to tap the top of the valve stem to get the core to present its threaded end. You may need to use a knife point to pull it out of the stem. Often I can simply shake and tap on the stem until the end of the core presents itself. Pull the threaded end of the valve out as far as possible. Catch and hold it with a fingernail. Twist the nut back onto the valve core's threaded end.
If the valve does not seal and hold air pressure, loosen the nut and push a few drops of water into the valve stem to wash away any shreds of rubber that might be blocking the valve. Give the water an assist by pushing and pulling the valve core back and forth in the valve stem. Or, press on the core so a significant amount of air escapes from the tire. That usually blows away whatever kept it from sealing. Then fill the tire with air to the desired pressure.
In my experience, the combination of Slime and a tire tube is not forever. After a couple of years the tubes often develop a slit or another leak that the Slime cannot seal. I do not try to save the Slime in the old tube, but discard both the tube and the Slime. Slime has a limited useful life, anyway.
One morning I was seven miles from home on my 14 mile bicycle route. Some puncture vines had blown their way into the middle of my lane. Normally, I would simply have ridden around them, but there was an oncoming automobile and I went right through the puncture vine. I stopped and picked numerous goat head thorns out of my two tires. My tires looked like a teenager with acne. There were green dots of Slime coming up out of my tires everywhere. But, my tires sealed and I rode home with no flat tires and plenty of tire pressure. I continued to ride on those tubes for quite a long, long time.