This repair assumes you are patching your tube. Use regular tire repair patches and glue. The peel-and-stick patches don’t conform well to the shape of tubes and tend to come unstuck as the tube is re-inflated inside the tire. They are also a very temporary repair which can fail on subsequent rides. Regular patches are good for the life of the tube if applied correctly.
Preparation
Clean as much dirt from the tire and rim before you start the repair. Remove the wheel from the bike (remember to release rim brakes first) and deflate the tube completely if it still has air in it.
Tire and tube removal
Push the tire towards the center of the rim all the way round on one side. This allows the tire bead to sit in the middle of the rim, giving you more room to pull or lever it over the rim.
Start trying to remove this side of the tire by “rolling” it off the rim with your (gloved) hands. If this doesn’t work, find your plastic tire levers (I’ve found Pedros to be by far the best), and insert two of them under the tire bead (which is still sitting in the center of the rim).
Lever both tire levers up at the same time so that the bead clears the rim. Now hold one lever still, and slide the other lever around the rim to pop the bead over the rim all the way around.
Once one tire bead is completely clear of the rim, you can remove the tube. Before you do so though, check to see if you can find the source of the puncture through the tire. This makes it easier to locate the place you need to repair on the tube. If you can’t find the source, remove the tube but keep it in the same orientation as the tire.
Find the puncture hole
Now, inflate the tube to find the puncture hole. Holding the inflated tube up to your face will allow you to feel where air is leaking. Water (or spit) will bubble when placed on the hole. Look on the same location on the tire for any remnants of the thing that caused the puncture. Also run your (gloved) hand carefully around the inside of the entire tire to find and remove any other spikes. The last thing you want to do is to have the same object puncture your repaired or replaced tube.
If you find a hole or pair of holes on the side of the tube, it is most likely a snake bite puncture caused by the rim pinching the tube against a rock you rolled over. Run a higher pressure to prevent this kind of puncture.
Puncture repair
Hopefully you’re carrying a patch kit – Park and Rema both make good kits. Clean and roughen the area around the puncture hole on the tube, make sure it’s completely dry, and then put a layer of tube patch glue on it, slightly larger than the size of the patch. Wait for the glue to become cloudy and dry to the touch. It is contact adhesive, so it won’t work unless it’s dry.
Peel the foil off the patch but leave the clear plastic bit on the other side. Now place the patch on the glue (rubber side down, clear plastic side up) and press hard for about 30 seconds. Don’t try removing and re-placing the patch once it’s touched the glue – this won’t work.
Leave the tube for another five minutes for the glue to set (longer in cold climates), then inflate it just slightly. With one bead of the tire on the rim, replace the tube in the rim, starting at the valve stem.
If you don’t have a patch kit, check out some alternative ways of repairing your flat tire.
Once the tube is repaired, start the second tire bead back on the rim at the side away from the valve. Put it way down in the center of the rim to give you more “play” once you have worked the rest of the bead on to the rim. Rest this piece against your belly, and use both hands at the same time to hook the bead back over the rim all the way round to the valve. You should not need to use the tire levers to put the tire back on. Use your (gloved) hands to roll the bead on. Using the tire levers will most likely pinch the tube and cause it to puncture.
Once the tire is back on (yes, it’s hard sometimes, but it came off, so it is definitely possible to get it back on), ensure that the tube is not trapped at any point under the tire bead, then inflate to 10-15psi (very soft). Now run your hands around the tire, squeezing it as you go. This allows the tube to seat within the tire, and ensures that it is not pinched anywhere. Now continue to inflate the tube. For a newly repaired tube, inflate the tire to 45-50psi (hard) or higher if your tire suggests. This uses the tire to press the patch securely against the tube.
Re-insert the wheel, re-attach your brake cable (rim brakes) and ride!
Tip: Out on the trail, you probably want to replace the tube using the spare you carry rather than patching it. Still check around the inside of the tire for spikes before using the new tube, or you’ll be patching that one too.