Keeping tires properly inflated is one of the simplest and most important things you can do for your bicycle. Tire pressure is measured in pounds per square inch (PSI). Road bikes require 90 to 100 PSI, mountain bikes 40 to 60 PSI, and hybrids 60 to 80 PSI. When riding, be sure to bring a spare inner tube and patch kit, in case you get a flat tire.
How to Fix a Flat Tire
1. Press brake pads against rim, and lift the cable from the brake arm.
2. Open quick-release lever. For the front tire, lift fork away from the wheel, loosening the adjustment nut if necessary. For the rear tire, pivot the derailleur back so gears clear the rim.
3. Insert a tire lever between rim and tire (on the opposite side of the wheel from the valve stem); lift the side of the tire over the rim.
4. Slide second tire lever along rim, and lift the rest of the tire's edge over the rim.
5. With only one side of tire lifted over the rim, pull the tube out. Inspect the tire; wipe off any debris.
6. Find the hole by pumping air into the tube and listening for a hissing sound. Using sandpaper, roughen the area around the puncture. Apply glue liberally to the area; let it dry, about 5 minutes. Place a patch over the puncture, black side up, and press firmly.
7. After a few minutes, give the tube enough air to take shape. Insert the tube's valve stem in the hole in the rim, and position the tube in the tire.
8. Using both thumbs, lift the side of the tire back over the rim. Pump 12 to 15 strokes of air into the tube, to help it seal itself properly; let the air escape.
9. Pump the tube to the recommended air pressure. Reinstall the wheel, and close the quick-release levers. (For the back wheel, pivot derailleur out of the way again; lay top of chain on top of cluster, and place bottom of chain under cluster.)