| If you think you have a flat, stop riding. Even if there’s still some air pressure in the tire, stop riding your bike, otherwise you'll damage the wheel rims. |
Empty the remaining air from the tube by removing the valve cap by pressing on the valve.
Remove the wheel from the bike by releasing the brakes and the quick release at the hub. If your wheels are not quick release but rather held on by nuts, loosen then with a 15mm wrench. Try to avoid using a crescent wrench because if it's not set correctly, a crescent wrench can strip the nut.
Remove the tire from the rim. Use a plastic tire lever to move the lip of the tire over the rim, on one side of the wheel. Do not use a screw driver. It will likely do more harm than good. Place one tire lever under the tire to bring the tire edge out. Use another tire to lever to slide around the rest of the rim to release the rest of the tire.
With one side of the tire open, pull the tube out and inflate it like a balloon. Listen for the rushing air to find the leak. Don’t dip it in water, that will just make it harder to stick on the patch later on. If the hole is a blowout or the valve stem is torn you'll have to replace the tube right away, but most of the time you can patch it. Once you’ve found the hole, mark it so you don’t have to find it again.
Prepare the tube for the patch by scouring it with the sandpaper provided in the patch kit. The scraping will allow for better glue bonding.
Modern patches work just like a sticker. Just stick it on over the hole. If your patch requires glue, apply the glue to the tube in a thin coat on an area larger than the patch. Allow the glue to dry before applying the patch. You will not get a good bond on the patch if the glue is wet.
Some patches will have a plastic backing. Do not remove the backing until after you’ve applied the patch. Apply the patch to the tube, and press it down firmly. Keep pressure on the patch for about a minute. Then remove the clear plastic. If the patch comes off when you remove the plastic, you need to rework your patching (better sandpapering, more glue, wait longer for glue to dry, apply pressure for longer period of time).
Before you replace the tube in the tire, find the cause of the flat. If whatever caused your flat is still in your tire, you'll get another flat right away. Match the location of the leak in the tube with the coordinating location on the tire and look for the cause. If you don’t find it, run your finger slowly through the inside of the tire feeling for what caused it, a tiny bit of glass or nail. If you don’t find anything, check the rim of the wheel itself for sharp spots or exposed spoke nipples.
Or, is there a hole in the side of the tire? I warn tire can cause a tire to pop. Improperly adjusted brakes may press against the side of the tire instead of the rim. That brake pad rubbing can wear a hole in the side of a tire really fast. If so, you'll need to replace your tire. In an emergency you can place a "boot" between the tube and the tire, using a dollar bill,or a cut pieces of an old tube.
Put a little air in the tube to give it stable shape, and put it into the tire. Reinstall the tire on the rim. Replace the valve through the valve hole in the rim. Push the lip of the tire into the wheel rim. You may need to use a tire lever for the last bit. Be careful not to pinch the tube between the tire and the rim, especially when you’re using the lever. You may need to release the air from the tube if it's too difficult to get the tire on the rim.
Inflate the tire to the recommended PSI (it's usually stated on the side of the tire) and replace the valve cap. Install the wheel back on the bike. Make sure the quick release is tight enough. If there are nuts, be sure when you tighten them that the wheel is aligned straight. If it's a rear wheel, make sure the chain is tight enough, yet has enough slack. If it's too tight the chain can bind.
Lastly, don’t forget to reconnect the brake cable.