1.Remove the wheel from the bike. The first thing you should do for any flat is to remove the affected wheel. Check the side of the wheel at the center of the spokes. If you have a quick release (which looks like a small lever), flip it over and spin it counterclockwise to loosen. If, on the other hand, you see a nut, you will need a wrench to loosen it. After this, disconnect the brakes, move the brake pads out of the way, and remove the wheel.

If you're dealing with the rear flat, you'll also have the chain and gears to deal with. Put slack in the chain by shifting into the smallest set of gears. Loosen the quick release or unscrew the nut holding the wheel in place as normal. If necessary, use your hands to pull back on the rear derailleur (the "arm" that the chain passes through containing the small pulleys) and/or maneuver the chain out of the way as you remove the wheel.

2. Use tire levers to remove the tire. When you've successfully removed the flat wheel, take the outer tire off. To do this, it can be helpful to use a sturdy prying tool. Some bike shops will sell small, specially-designed tools called tire levers for this purpose. Whether you use a tire lever or another tool, be careful not to pinch the tube and cause further damage as you work the tire away from the wheel. You can leave one lip of the tire over the wheel rim when you're done to make re-installation easier.

3.Locate the hole that's causing the leak. When the tire has been removed, pull the flat tube out from the tire and pinpoint the site of the puncture. This can be done in several ways — a few are listed below:

Inflating the tube and visually checking the surface of the rubber for holes

Mark the hole in the tube. Flat-causing tire punctures can be surprisingly small. Once you've found one, you don't want to lose it! Use a piece of chalk to make a "+" or "x" that intersects at the point of the puncture. If you're using a glue-on patch, make your mark large so that you can still see it after you've smeared on the glue.

If you don't have chalk in your patch kit, a ballpoint pen or any other sort of writing utensil will do. Chalk, however, is preferable because it's obviously easier to see white chalk on black rubber than blue or black pen.