Flat Tire Repair
You're thinking, "Who needs to be taught how to fix a flat tire?" Well, everybody. We all have to start somewhere.
If you get extremely frequent flats, see the options in our tire care section.
Of course, we're assuming you have a pump and patch kit with you. (And a spare tube, of course.) If not, start walking.
First step: If the rock or thorn didn't let all the air out of your tire, let the rest of the air out now.
On a cantilever (cable-pull) brake, push the cable down while holding the brake lever in against the tire. When the barrel comes loose, slide the cable away from the lever.On V-brakes, squeeze the two brake levers towards each other, then pop the cable guide up out of the retainer.
To remove the rear tire, shift the rear deraileur until the chain is in the smallest ring of your cassette (highest-numbered gear). Turn the bike upside down, then open the quick-release lever. Pull the wheel forward off the chain, moving the opposite side of the chain out of the way as the tire comes up.
Pull one side of the tire up, making sure the opposite side lies in the valley in the rim's center. Slide the tire lever down between the rim and the tire about 1/4 inch. Pull the lever down, exposing the bead of the tire.Trap the exposed bead of the tire with your thumb.
Run the tire lever around the entire rim. Leave the opposite side of the tire on the rim while you pull the tube out of the casing.
Tire levers have a notch that holds onto the spoke, so you can pry the tire bead out and hook the lever, then have hands free to go on to the next spot on the rim.
One trick I've used is to pass the tube in front of my wide-open mouth. I can feel the air with my tongue, and the turbulence makes a noise I can easily hear. A lick on the invisible leak shows exactly where it is.
For slow leaks, you may need to dunk the tube underwater and look for the bubbles.
Use sandpaper (preferred for bike tubes) or a patch-kit scraping tool to buff the tube. This is one of the most important steps. You must remove all oil, moisture, dirt, and talc. You must scuff the smooth tube surface so the glue can penetrate. Buff an area 1/4 inch bigger on each side than your patch.If the hole is near a seam on the tube, spend extra time buffing the seam flat.
Use only fresh and runny patch glue. If the adhesive has gotten old and gelled, the patch may not stick once the tire is inflated. Spread a thin coat of adhesive over the entire buffed area. Don't leave any deep spots. Let the glue dry for a couple of minutes.
The location of the leak in the tube gives you clues. If the hole is right in the middle of the outside curve, check the tread carefully. If it's on the side of the tube, check the tire's sidewalls. If the cut is on the inner curve of the tube, it may have been damaged by the spoke holes. Check your rim tape to see if there are any exposed edges.
The adhesive should be barely tacky. It shouldn't string or hold your finger.
If it's just a puncture, a standard 3/4-inch patch will do. If you have a slice, you'll need a patch at least 1-1/2 inch long. In general any slice longer than 1/4 inch won't hold a repair.
Peel the blue side away from the patch, holding a tiny corner of the patch with your fingernails. DON'T touch the rubber surface.
Press the patch very firmly into place. Squeeze at multiple locations to be sure all parts of the patch are firmly bonded.
If you have talc available, spread some over the exposed adhesive. If not, powdery dirt will do. This keeps the tube from bonding to the tire casing.
Starting at the valve-stem, push the casing under the rim. Move both hands simultaneously around the rim, seating the tire. When you reach the top, push the tire away from you to pull the last part of the bead over the rim. If the tire is tight, put two tire wrenches under the bead and gently lever the tire over the rim as shown.
And be sure to reattach the brake cable!