How to fit a dual tube system to a bicycle wheel that will enable you to deal with a puncture without having to remove the the wheel or need any tools other than a pump until you get home. When you get a puncture the second inner tube is sitting right there in the tyre waiting to be inflated.
Step 1: Drill hole
Drill a hole in the rim of the wheel for the second valve stem at about 1/4 to 1/3 of the way around the rim from the original one. If your drill finds the going hard, start of with a small drill bit and gradually work up in size.
Step 2: Preparation
Completely empty the air from one inner tube (roll it up and squeeze). Pump just a little air in to the other inner tube, this will make fitting easier.
Step 3: Place one side of the tyre over the rim
Place one side of the tyre over the rim and then insert the flattened inner tube as straight as you can. Next insert the slightly inflated inner tube - push back the flattened inner tube to get the valve stem in place then, working from both sides of the valve stem fold the flattened inner tube under the slightly inflated one (as shown in the picture) as you work your way around the rim. It takes a bit of fiddling, I never claimed it was easy.