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How to Fix a Flat Bike Tire

Home » Mountain Biking » Mountain Bike Repair » How to Fix a Flat Bike Tire

To fix a flat bike tire, you'll need a pump, and a patch kit that includes a tire lever, sandpaper or a scraping tool, glue, patches, and possibly talc. You also may want to carry a spare tube, in case the damage to the original tube cannot be repaired.

The first step is to remove the tire from the bike. Most modern mountain bikes have quick-release front wheels, and relatively quick-release back wheels. To remove the back wheel, shift the rear derailleur so that the chain is on the smallest gear. Turn the bike upside-down before opening the quick-release lever; then pull the wheel forward off the chain.

Go all the way around the circumference of the wheel, removing the tire casing (the outer layer of the tire) from the metal rim by squeezing the two sides of the casing to the small valley in the center of the rim. Then pull one side of the tire up, and insert the tire lever between the rim and the tire, about 1/4 inch in. Pull the lever down to expose the bead of the tire. Hold on to the bead with your thumb.

Gently run the tire lever away from your thumb and around the wheel's rim. Leave the other side of the casing in the little valley in the middle of the rim. Pull the tube out of the casing.

Next, you will need to find the leak in the tube. Pump the tube up and run your fingers along its surface until you find the spot where air is escaping. A slice in the tube longer than 1/4 inch will probably not repair well, in which case you may want to go ahead and use your spare tube. If you can't find the puncture in the tube, submerge it in water and look for bubbles.

Buff the surface of the tube around the leak with sandpaper. This removes oil and dirt, and scuffs the tube's surface, which helps the glue to bond the patch to the tube. Buff an area slightly larger than the patch you are going to use.

Spread the patch glue on the whole area that you have buffed. Patch glue should be fresh and runny when you first squeeze it out of the tube, so replace the glue in your patch kit if it gets old or too thick. Let the glue dry for a couple of minutes before you apply the patch.

The tube is ready for the patch when the adhesive is barely tacky. Test it by touching an area on the edge of where you've spread glue. Peel the blue side away from the patch and apply the patch to the tube. Do not touch the rubber side of the patch. Once it's on the tube, press and squeeze the patch until it’s well bonded to the tube. Use a little talc or powdery dirt on the exposed glue around the patch to keep the tube from sticking to the tire casing.

Now replace the tube under the casing. Make sure you have the valve stem straight in its hole. After replacing the tube, start with the valve stem at the bottom of the wheel, and push the casing back under the rim all the way around the wheel to the top.

You can pump the tire to check your repair work. Replace the wheel, and don't forget to reconnect the brake cable.

Next Page: How to Use a Chain Tool

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