Mending a puncture
Having a puncture can be annoying, but it should be easy to fix. If you are not used to fixing punctures it can take some time, but does get a lot quicker with practice. It is generally faster to replace the inner tube with a spare rather than try to patch a tube that is on the bike. (You can repair the punctured tube at home or at your workplace.) Puncture glue takes at least five minutes to dry properly.
If you get a puncture, first check the tyre to see if you can find anything that may have caused the puncture. If there is something obvious you may be able to pull out that section of the tube and patch the spot without removing the wheel and then the tube. If you cannot find the object that caused the puncture remove the inner tube, inflate it and listen, or feel, for escaping air. Once you have established where the air is coming from, check that section of tyre for a piece(s) of glass or other sharp object(s) and remove it. There is no point in replacing an inner tube only for it to be punctured again.
Many people choose to use puncture resistant tyres, which have protective strips of materials such as Kevlar inside them.
Removing the inner tube
Remove the wheel, undo the valve cap, remove the threaded metal collar (if there is one), empty any air out of the tube and push the valve back into the rim.
Fit 2 or 3 tyre levers into the rim about 2cm apart and pull them back, levering one side of the tyre out and over the side of the rim.
Take care you are not pinching the tube while you lever the tyre out. Remove the middle of the 3 levers, and hook it under the tyre about 2 cm past one of the other two. You then have 3 levers in place again, but a longer section of the tyre is hooked over the rim.
Take the middle lever out and repeat the process a few times. Once about a third of the tyre is hooked over the rim, the remainder will come off more easily.
The tyre should remain sitting on one side of the rim. Grab the inner tube at the valve hole, push the valve up through the rim and pull the valve out from the tyre. Pull the rest of the inner tube out.
Mending the puncture
To find the hole you can either pump the tube up and feel/listen for the air coming out or hold the tube under water and see where bubbles appear.
Deflate the tyre, clean the area around the hole and make sure it is dry.
Lightly sand the spot round the hole, and mark the hole with a ball point pen, chalk or a dab of rubber solution.
Apply a little more rubber solution until you have an area slightly larger than the patch, keeping the hole in the middle all the time. Let the rubber solution dry (5 minutes) but don’t let any dirt stick to it.
Peel off the backing paper/foil/plastic on one side of the patch and be careful not to get dirt or fingerprints on the patch itself. Place it on the inner tube so that the middle of the patch covers the hole, and make sure that the patch is in good contact with rubber solution all around the edge. Squeeze the patch hard into the rubber solution for about a minute.
To remove the backing paper (not an essntial task) fold the inner tube in half so that the backing paper on the patch splits down the middle. Carefully peel the backing off from the middle towards the edge to avoid lifting the edge of the patch.
Dust the top of the patch and any exposed areas of rubber solution with chalk/talc to stop it sticking inside the tyre.
Finally, give the inner tube 2 or 3 strokes of the pump before putting it back on the wheel. This prevents the tube getting pinched when you put the tyre back on.
Replacing the inner tube
Starting at the valve hole, put the inner tube onto the rim under the tyre. Then hook the tyre back onto the rim with your hands, making sure that the inner tube does not get pinched, and that the tyre is seated properly on the rim. You may need to use a tyre lever to get the last section of tyre back on the rim. Replace the threaded collar, pump up the tyre and replace the dust cap.