CO2 cartridges and inflators

The fastest roadside fix there is

A CO2 cartridge reinflates a tyre in three seconds, with no effort and taking up barely any space. It's the tool for racing and quick rides. But it has two characteristics you need to know about before setting off with one — and few people do.

CO2 doesn't stay in the tyre

The CO2 molecule passes through the tyre rubber much faster than air. A tyre inflated with CO2 loses most of its pressure within 24 to 48 hours. That's not a leak: it's normal. After a CO2 roadside repair, the tyre therefore needs to be re-inflated with air as soon as you get home, before putting the bike away. It's the number-one reason behind ‘my tyre went flat again on its own’.

CO2 and tubeless sealant

Expanding CO2 is extremely cold, and the cartridge can cause the sealant to coagulate inside the tyre. The sealant then loses its ability to seal punctures, just when you need it. If you ride tubeless with sealant, use CO2 only as a genuine last resort, and plan to check and top up the sealant afterwards.

16 or 25 grams

• 16 g : the standard size for road and gravel riding. One cartridge brings a 25 to 32 mm tyre up to a rideable pressure.
• 25 g : for mountain biking and wider tyres, which have a much greater volume. A 16 g cartridge won't inflate a 2.4-inch tyre enough to get you home.
• Threaded : every cartridge in this range is threaded, the current standard, ensuring compatibility with the vast majority of inflators. Older unthreaded cartridges require a specific inflator.
• Carry one more cartridge than you think you'll need : there's no second try with CO2, and one wrong move wastes the whole cartridge.

Choosing your inflator

An inflator with controlled flow (dial or trigger) lets you release the gas gradually, stop, check and carry on. It costs a little more than an all-or-nothing inflator and helps avoid wasting a cartridge. Some models include a pressure gauge, while others combine with a mechanical mini pump — belt and braces for anyone who doesn't want to walk home.

Precautions

The cartridge gets extremely cold becomes freezing cold as the gas expands: don't hold it in your bare hand; use the insulating sleeve supplied with most inflators. And bear this in mind before travelling: airlines restrict CO2 cartridges on board aircraft, in both checked and cabin baggage, depending on the airline.

To find out more: How to fit tubeless tyres

See also: Handheld bike pumps · Puncture sealants · Multi-tools