What CO2 inflation is good for
A CO2 inflator fills a tire in seconds, which makes it handy for roadside flats and races. It is small and light. The downsides are that each cartridge is single use, that it is easy to add too much gas in one go, and that the gas typically seeps through the tube faster than air does.
Cartridge types and sizes
Cartridges come in a few forms.
- Threaded: screws into the inflator head. This is common and the gas flow is usually easy to control.
- Non-threaded: pierced by a push-on or lever-style head.
Cartridges are sold by the weight of gas, in grams. Small sizes are usually used for narrow tires and larger ones for wider tires, but the numbers vary by brand and by tire volume. A cartridge that suits a slim road tire may not fill a wide mountain bike tire to a useful pressure.
About CO2 charts
Many readers search for a chart that says which cartridge gives which psi. These charts do exist, and the major brands publish their own. Treat any chart as approximate, because the result depends on:
- the tire’s internal volume (width and wheel size),
- whether a tube is fitted or the tire is tubeless,
- the starting pressure,
- temperature, and
- how fully the cartridge empties.
Use the cartridge manufacturer’s chart for your tire size and then confirming the actual pressure with a gauge. If you cannot find a chart, partially discharge, check, and add more if needed.
How to use an inflator
- Check your valve. Presta needs the small nut unscrewed first, and a head made for Presta. See pumping up a tire with a small (Presta) valve.
- Seat the tire. If you have just fitted a tube, make sure the tire bead is in place on both sides.
- Attach the head firmly to the valve.
- Fit the cartridge. With a threaded cartridge, screw it in to start the flow. With a controllable head, open the flow in short bursts.
- Stop when the tire feels near firm. Detach the head with care.
- Close the valve and replace the cap.
- Check pressure with a gauge as soon as you can, and adjust.
Safety: cold cartridges
Releasing CO2 makes the cartridge and head very cold, and they can cause a cold burn on bare skin. Use the protective sleeve if your inflator has one, hold it carefully and do not point it at yourself or anyone else. Do not carry used or full cartridges in a hot, closed car, or store them near heat.
Afterwards: check pressure
CO2 can leave you with more or less pressure than you wanted. When you reach home, check with a gauge. Some riders let out the CO2 and refill with air, particularly for tubeless tires, because CO2 may mix with some sealants differently. If this matters to you, check the sealant maker’s guidance. For general pressure advice, see how to inflate a bike tire properly. To release extra gas, see how to safely deflate a bike tire.
Choosing an inflator
- Look for a head that supports your valve type.
- A head with flow control gives you more precision.
- Pick cartridges sized for your tire width, and carry a spare.
- Keep a small pump as a backup, because a failed cartridge or an error with the head can leave you stranded. If you ever have to inflate without a pump at all, see inflating a bike tire without a pump.
FAQ
Is 20 psi too low for bike tires? For many road tires it would be below the printed range. Some wide, off-road tires are run at low pressures. Check the range on your own tire.
Is a 28 inch bike tire the same as a 700c? They are close and often treated as interchangeable in casual use, but the labels come from different systems. Check the ETRTO size (for example 622 mm bead seat diameter) printed on the tire to be sure.
How do I use a CO2 cartridge? Attach the head to the valve, fit the cartridge, release the gas in short bursts, then check pressure.