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  How to Fix a Flat Tire Excerpted from the Essential Cyclist by Arnie Baker
  By following these instructions, most of you should be able to fix a flat in under 10 minutes. Experts can fix one in under 3 minutes. There are many other techniques for changing a flat, however, this is a thorough description for beginners.

Equipment Needed:

  • Tire irons
  • Spare tube(s)
  • Patch kit
  • Hand/frame pump or CO2 cartridges
  • If you don't have quick release, you will need the appropriate wrench to remove your wheel from your frame.
Here are the steps:
  1. Remove the wheel from the bicycle frame.
    If you have flatted your rear wheel, shift your rear derailleur to the smallest cog - that's the hardest gear, the one on the outside near the frame. This will make removing the rear wheel easier. The front wheel is the easiest to remove.

    Use the brake caliper quick-release mechanism to allow the tire to pass through the break pads. If you're using wide tires, you may need to loosen the brake cable to allow the tire to pass through the break pads. On some older bikes there is a bolt you may need to unscrew (if there is a tab on the fork that prevents the front wheel from coming off accidentally). Bolts loosen counterclockwise and tighten clockwise.

    Check the tire for glass, thorns, nails slices etc. before you begin step 2.

  2. Remove one side of the tire from the wheel.
    Take off valve washer and nut. Open the valve and if air remains in the tube, deflate the tube completely.

    Insert the tire iron under one side or bead of the tire at the point farthest away from the valve. Pry the side of the tire off the rim and slide the tire iron along the rim to roll off the rest of the bead of the tire. Use plastic tire irons designed for this job, not screwdrivers or other objects, which can result in more tube punctures. Leave the inner bead of the tire setting on the rim. If after placing the first tire iron you are unable to slide it, use 2 tire irons to work the tire edge off. Free the contact between the tire edge and rim lip, compress the tire to the center hollow of the rim and force the tire to the other side of the rim.

  3. Remove the tube.
    Pull out the tube, finishing at the valve. Once it's out, keep the orientation of the tube constant with the wheel. This will further help you identify the cause after you've found the leak if it wasn't obvious when you checked the tire prior to step 2.

  4. Find the leak.
    Pump up the tube. You'll probably hear the hole before you see it. Pass every inch of the tube by your ear to detect the leak. If that doesn't work, pass the tube by your mouth and you may feel the escaping air on your upper lip. Placing the tube in water will show you the trail of bubbles to the hole.

  5. Determine cause of flat.
    It is important to find the cause of the flat. If you don't and the object remains in the tire, you'll probably flat immediately again. One method is to hold the tube up to the wheel to determine the position of the problem (that's why the original orientation of the tube/tire is important). The leak may correspond to a foreign object stuck in the tire or to slippage or tear of the rim tape on the inside of the wheel. It's not always possible to find the cause, but here are some things to look for:
    Punctures: check the tire for thorns, glass, nails etc., especially where the hole in the tube was found. Feel the inner surface of the tire carefully to locate the cause and remove it.

    Snakebites: Snakebite flats are usually caused by the tire and tube being pinched between the road and the rim, causing 2 small holes in the tube that can look like a snakebite. The cause is generally under inflated tires, too narrow of a tire for your weight, or hitting a rock or pothole while having your full weight on the tire. Make sure your tires are properly inflated before each ride, use a larger size tire if you weigh a lot, and try to avoid rocks and potholes.

    Pinched tubes: This happens when a bit of your inner tube is pinched between the tire bead and the rim. It is usually caused by an error in mounting the tube and tire although occasionally a tire defect or mismatch between rim size and tire size is to blame.

    Less common causes: Inadequate rim tape over the spoke holes causing the tube to push through the hole and burst, spoke ends that protrude through the rim strip/tape and puncture the tube, valve failure and tube failure are other causes.

  6. Check tire.
    You've already run your finger along the inside of the tire to check for thorns, glass or other causes. Check again. Also, examine the tire for defects, threads showing, sidewall slices or brittleness. Some tire problems can be temporarily covered/supported/booted with a tube patch, dollar bill or food bar wrapper. Large holes or slices are unsafe for riding and your tire should be replaced ASAP.

  7. Replace or patch the tube.
    Most riders out on day rides, especially on group rides, have a spare tube and simply replace the tube. This takes much less time than patching. The tube can be patched after the ride is over. Do carry a patch kit in case of a second flat. To patch a tube, follow the instructions in the kit, which should be as follows:

    Roughen the surface around the hole in the tube with the sandpaper from your patch kit (tube must be dry). Apply the glue over an area larger than the patch you will use and allow it to dry for about 5 minutes. Without touching the surface of the patch, remove the foil backing and apply the patch to the tube and hold until set. Inflate tube and check for other holes. You can also use "glueless" patches, they cost more and don't form a permanent seal as glue-on patches do, but they are a temporary, convenient and quick alternative.

  8. Place new or patched tube under the tire, on the rim.
    Inflate the tube just enough for it to hold its shape. Too much inflation and it won't fit inside the tire. Too little, and you are likely to pinch it while installing the tire. If using a new tube, remember to remove the nut/washer from the valve stem. Insert the valve stem and fit the tube inside the tire, all the way around.

  9. Replace the tire on the rim.
    Reattach the tire to the rim, starting about 90 degrees away from the valve stem. Work the tire onto the rim moving first toward the valve stem. Finish away from the valve stem. Just before you are finished installing the tire, deflate the tube. Use both thumbs and middle fingers to roll and push the last part of the tire over the rim. Tires are often a tight fit, so this can be the most difficult part and takes some practice. Try to avoid using the tire irons, since it's easy to puncture a tube with them.

    Press the valve stem through the rim back up into the tire and allow it to return downward. This helps correctly seat the thicker valve stem area within the tire, preventing it from being pinched. Inflate the tire a bit (about 20psi) and move the tire back and forth, going all around to make sure no part of the inner tube is pinched. Inflate the tire to its rated pressure. You'll need to estimate how much air to pump in by feel (or when you get tired pumping!). Remember to close the valve on the presta valve when finished.

  10. Finally. Replace wheel on bike frame.
    To replace the rear wheel, pull the derailleur backward, set the smallest cog on the chain, release the derailleur and pop the axle in the dropouts. Tighten the brake cable and/or bolts if you loosened them, tighten quick release levers and close brake pad levers. Check that the wheel is seated and centered on the frame between the chain stays and between the brake pads.
Special Notes:

Presta valves are skinny, Schraeders are thicker.

If you find that you are fixing flat after flat after flat, it's pretty frustrating. Sometimes you have to replace the tire as well as the tube to break the cycle because of a thorn or piece of glass that you just can't find.

While using a hand pump, be sure to keep it steady with your thumb positioned over the tire. It is possible to break a valve stem by forcefully bending it while pumping. Steadying the wheel against a solid object, such as a wall, makes inflating easier.

To prevent flats, keep your tires properly inflated, check your tires before each ride, replace old, worn tires, and check your rim strips every 6 months or whenever you have a flat. Watch for (and avoid) glass and sharp objects, especially in the "unused triangles" at intersections.

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