How to Fix a Flat Bike Tire

mj-618_348_how-to-fix-a-flat-bike-tire
 Harold Cunningham / AFP / Getty Images

If you ride a bike, you're going to get a flat tire eventually. Thankfully, changing a tube can be fast and easy with a little know-how and practice. And you can also take steps to prevent them before you start your ride.

Prevent Flats Pre-Ride
"Many flats can be avoided with just a little routine maintenance," says USA Cycling-certified race mechanic Matt McKinney. First, inflate your tires before every ride to prevent pinch flats. When your tires are underinflated, they can bottom out on a pothole or large rock, pinching and puncturing the tube between the rim and tire. The resulting puncture looks like a two-hole snakebite in the tube. For your road bike, McKinney recommends keeping your tires between 80-100 psi, depending on the ride (lower pressure in bad conditions to improve grip) and your weight (heavier riders need more air).

When pumping your tires before a ride, take a moment to spin your wheels, looking for bits of glass or debris that might be working their way through the tread. Also look for any flat spots that could indicate excessive tire wear. Tires have life of about 5,000 miles.

Pack the Perfect Flat Kit
Always ride with a tire lever, patch kit, spare tube, and inflator, be it a frame pump or a CO2 head and cartridge. Most riders typically just replace the tube, using the patch kit only if they flat again later in the ride. You should also bring along a dollar bill (a gel or energy bar wrapper works too) that can be used as a makeshift boot in case of a sidewall tear in your tire — slipping the boot between the new tube and tear prevents the tube from popping out.

Find the Cause of Your Flat
If your rear wheel is going flat, shift down into your small front ring and the smallest cog on the rear cassette — this makes it easier to get the wheel off and back on. Then flip the bike upside down to remove the wheel. 

Pry the first tire bead off with a tire lever, then run the lever around the rim to fully remove it. Remove the old tube and second bead as well. Before installing the new tube, locate what caused the puncture. If you have trouble locating the cause, turn the tire inside out. "Running your fingers around the inside of the tire is the fastest way to find the glass or debris, but it's also a good way to cut yourself," McKinney says. Instead of risking injury, he suggests packing a small rag to locate the cause. "You can also wrap your spare tube with the rag, so it's better protected against other items accidentally puncturing it." Also, use this time to check your rim tape. If the tape shifted, a sharp, exposed spoke hole could be the culprit.

Install and Inflate the New Tube
After removing the debris, work one tire bead back onto the rim. Using your mouth, inflate the new tube enough that it takes shape — this keeps the tube from popping out under the bead. Then work the tire all the way back onto the rim. McKinney recommends lining up the tire markings with the tube's valve stem. "The next time you flat, you'll be able to find the failure on the tube, then trace it back to the correct spot on the tire or rim strip," he adds. 

Working the second tire bead back onto the rim takes a bit of hand strength. Avoid using a tire lever, as it could catch and puncture the tube. After kneading the tire back on, give it a quick inspection to make sure that it's fully and correctly seated on the rim, with no bits of tube sticking out from underneath.

If everything looks correct, re-inflate the tube. If you hear popping noises, don't worry; it's just the sound of the tire seating on the grooves of the rim. As the tube inflates, keep an eye out for any bulges. The tire should be uniformly smooth and even. After the tube is fully inflated, put the wheel back on the bike, making sure it's sitting evenly between the brake calipers. Close the quick release and get back to your ride.