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by Claire Lunardoni
Glass, rocks, road debris, insufficient tire pressure and improper inner tube installation can all lead to a flat tire. A puncture can happen without warning, so carry a flat kit on every ride. Changing a flat quickly and without puncturing the new tube takes some training, so practice at home before you need to on the road.
Removing a Punctured Tube
Step 1 Release the brakes to create the clearance to remove it from the frame. On most road bikes, a lever on the calipers releases the brakes. Release mountain bike and hybrid brakes by squeezing the brake arms together, and freeing the noodle--the brake cable casing--from the bracket that holds it in place.
Step 2 Open the quick-release lever near the axle, and unscrew the bolt on the opposite side to release the wheel from the frame. Bolts secure the wheel on some older bikes, and require a multi-tool to loosen. To remove the rear wheel, balance the bike upside down on its seat and handlebars, and pull the chain clear of the cassette as you take the wheel out.
Step 3 Unscrew the valve cap, and depress the valve to release remaining air from the tube.
Step 4 Insert the curved end of the tire lever under the tire lip, and slide it all the way around the rim to pull one side of the tire free of the rim. If the tire keeps popping back into the rim, insert one lever, and use the hook on the opposite end of the lever to affix it to a spoke. Use a second lever to release the tire from the rim.
Step 5 Remove the punctured tube from inside the tire.
Installing a New Tube
Step 1 Run your fingers along the inside of the tire to find the cause of the flat. Remove any embedded glass, thorns or debris from the tire to prevent further punctures.
Step 2 Use your pump to slightly inflate the new tube. Inflating the tube prevents it from twisting as you seat it inside the tire. Thread the valve stem through its hole in the rim first, and then place the rest of the tube inside the tire.
Step 3 Seat the loose lip of the tire back into the rim with your hands. Once it is in place, check that the tube is not protruding from beneath the tire, because the tire can pinch it against the rim when you inflate it.
Step 4 Inflate the tire to its recommended pressure. The tire should feel hard on a road bike, and squishy on a mountain bike.
Step 5 Replace the wheel in its grooves or and secure the brakes.
Tips and Warnings; When changing the rear tire, shift to the smallest cog, or gear, in the rear before removing it. Pumping your tires to the recommended pressure printed on the sidewall before every ride will help avoid flats. If you intend to patch the punctured tube, fix the flat with a new tube, and patch the old one when you get home. Avoid using tire levers to replace the tire into the rim, since the levers can puncture the new tube.
Things You'll Need; 2 tire levers, Inner tube, Bicycle pump
References; Bicycle Universe: How to Fix a Flat Tire on a Bicycle. Bicycle Maintenance Manual; Eugene A. Sloane; 1977
Read more: http://www.livestrong.com/article/176049-change-bicycle-flat-tire/#ixzz26O830Pmd