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.
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Signing UpStep 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.
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An alternative to double-stuffing your tire with a second tube (and having to do the jiggery-pokery necessary to have the valve of the outer of the two come through any extra hole in the rim) is a variation on 'toughy tape': cut away the beads and most of the side-walls from both sides of a scrapped--even bald--tire of a size to just fit inside the tire you already have on the rim, and lay that in before installing the tube and closing things up by installing the second bead of the whole tire.
The re-used tire's tread, in this case, is integral i.e. unbroken/uncut, at least along the center line. Choosing the proper size is important, though, as tires don't stretch much at all. If you're using 27" rims, choose a scrap tire from the 700 class. If you're using 700s, you'll almost certainly have to go with a much smaller width tire e.g. a 700x32C tire will need something like a 25C's carcass.
Another consideration for the bead-removal operation is the extent to which the edge that remains is 'feathered'; if you angle the cutting strokes in such a way that the edge is tapered, it's much less likely that that edge will cause any grief to the tube.
With this method, you are inserting an integral, second layer of fairly dense rubber between the tube (thin-walled, generally, and containing air under pressure) and the tread of the tire. Rubber cuts (or is most easily punctured) when it's wet, so having a layer of thick rubber, acquired costlessly, between the (possibly wet) tire and the under-pressure, thin-walled innertube means that anything that does get through the outside layer, will have also to pass through a fairly thick, almost-certainly-dry layer of rubber before reaching the vulnerable (but repairable) innertube. This arrangement should greatly reduce the likelihood of a flat, ceteris paribus.
Obviously, the downside to this approach is that that liner will have a mass, that mass will be at the circumference of the wheel, and you'll, therefore, have to accelerate (and decelerate) that mass in perpetuo. There's no free lunch--but you knew that.
As for slime, I don't recommend it, generally; I've found that its presence tends to make patching any eventual hole in the tube more difficult.
Although If you want to make your bike tyres almost close to invincible, line the inside of the tyre with the Seatbelt from a car, the weave is so tight on a car seatbelt (to pass safety requirements) that a thorn wont get through it, especially not a nail.
unless you are breaking the sound barrier on your pushbike!
I grew up in rural Australia where the thorns and Bindys are huge, and using a good quality thick inner tube and the seatbelt, I only changed about 3 pushbike tyres in my life.
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I don't work for them, but their stuff is quite good. I would HIGHLY suggest checking out their video segments!
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