Somewhere down the road, you're going to get a flat. But come prepared with a few simple gear items—mini air pump (or CO2 quick-fill cartridge), tire levers and spare tube or patch kit—and arm yourself with a little know-how, and it only takes a few minutes to fix and continue on your merry way. Here's how.
Remove The Tire
Depending on your level of fix-it experience, you may want to remove your wheel, so you have more room to work. To do so, first release your brakes (usually by flipping a quick-release lever or squeezing the calipers together and releasing the pull-cable from the notch where it hooks on the caliper arm). Next, release your wheel by opening the quick-release lever on the axle, or use a wrench to loosen a bolt-on axle. With the back wheel, you'll have to untangle it from the chain, which is easier if you're shifted into the smallest chainring.
The tire is held onto your wheel through a cominbation of grip from the bead—or tight outer edge—of the tire and air pressure from the tube. To pry the tire off, hook the rounded end of a tire lever (the black tool pictured above) under the bead of the tire and unseat it. Hook the other end onto a spoke, which holds the lever in place and keeps the unseated tire from popping back into the rim. Hook the rounded end of a second lever under the bead next to the first and shimmy it around the tire/rim clockwise (see below photo) until one side of the tire is completely off the rim.
Find the Leak
Start by slowly inspecting the outside of the tire. Usually, you'll find a pebble, glass shard or other sharp object lodged into the tire. If you don't see anything unusual, remove the tube, pump air into and listen carefully for the telltale hiss of a leak (if it's a super slow leak, you may need to submerge the inflated tire in water to find it—you'll see bubbles). Inspect the inside of the tire—paying careful attention in the area of the hole—to make sure whatever punctured your tube is gone. Don't see anything? Run your fingers carefully along to be absolutely sure. If there are two holes side-by-side, it's a "pinch flat" caused by your tube being pinched between tire and rim.
Patch or Replace the Tube
To patch: If it's convenient (and it rarely is), clean the punctured area of the tire with an alcohol prep pad or wet paper towel. Rough the surface around the hole with sand paper (included in most common patch kits). For a glueless patch, just stick it over the hole and press down tightly. For a glue-on patch, apply a thin layer of glue to the tube (some require you to glue the patch, too—just follow the included directions), and wait for the glue to get tacky. Apply the patch and press firmly.
To replace: Short on time? Simply remove the damaged tube and pack it away to fix when you have more time. It's practically criminal to throw it away at this point, as modern patches are very good, and can extend the life of a tube for hundreds or thousands of miles.
Install the Tube
Using your pump or CO2 cartridge, inflate either your tube (patched or new) until it holds its shape. Insert it into the tire and, starting with the valve stem, work the tire back into the rim. One bead should already be seated fully onto the wheel. With the unseated side facing you, roll the bead away from you and onto the tire, working your way around the wheel in both direction with both hands (this takes a bit of elbow grease, to be sure). Don't use the levers to reinsert the bead, or you may pinch the tube and cause another flat. Once the tire is fully installed, check both edges to be sure the tube isn't pinched anywhere between the rim and tire bead. Inflate the tire completely, checking that the bead is seated correctly and the valve stem remains straight.
If you took it off, reinstall the wheel. Wipe your hands on your pants, pat yourself on the back and ride off into the sunset. You've just bailed yourself out of a serious jam, and saved yourself $10 or $15 (the average bike shop fee for fixing a flat).