It's a gorgeous day, and you're out on your bike. Then it happens -- a flat. Oh, you can fix a flat, but pumping up a tire with a pump that's small enough to fit on your bike is a hassle, especially a road tire, which requires high pressure. Enter the carbon-dioxide cartridge.
Fix a Tire in Nothing Flat
Even the best mini-pumps take forever, but in the blink of an eye a CO2 cylinder can deliver more than enough air to get you home. A 16-gram cartridge will put about 40 psi in a mountain bike tire and about 125 psi in a standard road tire. And they're small -- about one-sixth the size of a frame pump.
Cartridge systems come in two pieces: an adapter and a cartridge. Some adapters just get the air into the tube, but look for an adapter actually controls the flow of air from the cartridge.
TIP: Consider practicing using cartridges a couple of times before you road test your new system; it's a good idea in general, and using CO2 cartridges can be a little tricky at first.
Avoiding Pinch Flats
Putting too much air into a tube without making sure it's seated properly in the tire can cause a part of the tube to get pressed against the edge of the tire. When the air pressure reaches near maximum, that pressure on the tube can actually cause the tire to cut the tube's rubber, resulting in a "pinch flat." That's why you should put in about 20 pounds of air and then "massage" the tire (to help seat the tube in the tire and the tire on the rim) before you fill it to the brim.
CO2 cartridges are not always easy to control, even when the adapter can turn the air on and off, so it's a good idea to keep your pump with you. Use the pump for the first push of air, massage the tire, and top the tube off with the cartridge.
TIP: While a 16-gram cartridge may be necessary to get home safely on a mountain bike tire, it can deliver too much air to a road tire, especially if you pump some air in first. Consider carrying 12-gram cartridges for road tires; they deliver closer to 90 psi.
What's the Trade-Off for All This Convenience?
CO2 cartridges are single-use items, so it makes sense to keep a patch kit and a pump with you, just as it does even when you're carrying a spare tube.
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