Changing a flat tyre out on the road can be a pain in the neck but it's likely something that every rider will have to do at some stage. While it's advisable to carry a hand pump with you in case of a flat, for many riders the size and awkward shape is prohibitive, leading many to opt for a CO2 cartridge and inflator instead.
CO2 cartridges are much smaller and lighter than a hand pump, easily fitting into a saddle bag or jersey pocket. The cartridges are full of compressed air and can inflate a flat tyre in a matter of seconds with little effort. The drawback to using cartridges instead of a hand pump is if you get it wrong, there's no going back - once the air has been released from the cartridge, it's done. As a result, if you use CO2 cartridges or are thinking of making the switch, it's imperative you know how to use them correctly otherwise, that flat tyre could turn into a cab ride home, a phone call to your significant other for a lift or worse, a long walk in your cycle shoes.
What to know before we start
Here are a few basic terms that will help you with the process outlined below.
CO2 cartridge: Small metal container of compressed CO2.
CO2 inflator: Tool that accepts the CO2 cartridge, attaches to the tube valve and inflates the tyre. CO2 cartridges will either screw into the CO2 inflator or press into them to release CO2.
Threaded or non-threaded: As the name suggests CO2 cartridges are either threaded or non-threaded. Threaded cartridges screw into the inflator head whereas the non-threaded CO2 cartridges simply push in. Non-threaded cartridges are not as reliable as threaded ones and less common, but whichever option you decide on, make sure the CO2 cartridges match the inflator.
Flow control: Some CO2 inflators and pumps have a 'flow control', which, moderates the amount of CO2 released into the tyre. For units without flow control, it's all or nothing.
PSI: Unit of measurement for pressure. Measured in 'Pounds per Square Inch'.
Preparation
We are going to jump straight into inflating the tyre with a CO2 cartridge but if you want to know how to change a tyre in six easy steps, read our How to Change a Flat article.
To start with, put some air into your tube before placing it onto the wheel, this will give the tube some shape before you put attempt to put it into the wheel. You can either blow into it like a balloon or if you have a flow control CO2 inflator you can carefully put a little bit of air in.
Once you have put the tube back onto the wheel and the tyre is in place, it's important to check that there is no sign of the tube. Work your way around the wheel pushing the tyre into the rim well to ensure the tube will not be pinched when inflated.
Also worth noting is that once the CO2 is released, the cartridge and inflator head will get extremely cold, so it pays to wear gloves or buy CO2 cartridges with protective sleeves to protect your hands.
Getting the CO2 inflator right
Depending on which type of inflator you have, you will need to either screw the CO2 cartridge onto the CO2 inflator or screw the CO2 inflator onto the tube's valve. Some inflators require you to screw the CO2 cartridge to the inflator and then press the inflator head onto the valve to release the CO2. Others will release the CO2 as soon as you screw the CO2 cartridge onto the inflator, in which case it needs to be connected to the valve first. Make sure you check which inflator you have and use accordingly.
The inflation process
The inflation process will happen quickly, within a handful of seconds. The tyre pressure each CO2 cartridge can achieve will vary depending on the size of the cartridge and how well you perform the process. CO2 cartridges normally come in 16g, 20g and 25g sizes. See below for an guide of inflation figures based on cartridge size.
| CO2 Inflation Chart |
||||
|---|---|---|---|---|
| Tyre type | Tyre size | 16 gram Co2 | 20 gram Co2 | 25 gram Co2 |
| Road | 700 x 23c | 130 psi | 78 psi (2 tyres) | 90 psi (2 tyres) |
| Road | 700 x 28c | 88 psi | 106 psi | 125 psi |
| Cross | 700 x 35c | 58 psi | 70 psi | 80 psi |
| MTB | 26 x 2.4 | 27 psi | 32 psi | 41 psi |
| MTB | 27.5 x 2.25 | 22 psi | 26 psi | 32 psi |
| MTB | 29 x 2.1 | 31 psi | 43 psi | 46 psi |
You may have to moderate the amount of CO2 you release into the tube. The bigger cartridges can over-inflate and cause the tube to burst. As you inflate the tyre, be sure to keep contact with the tyre and a watchful eye. Once it is firm, it's time to stop inflating. It's hard to know exactly how much inflation is too much when doing it by touch or sight but the more you do it, the easier it will be to know when it's at the desired pressure.
Once you've finished inflating your tyre remove the empty CO2 cartridge from the CO2 inflator and either place it in your jersey pocket or put it in the nearest bin. Don't leave it on the side of the road for someone else to pick up.
The next day you'll more than likely find that your tyre will be flat (or well on its way to being flat) within 24 hours because CO2 will leak out of your tyre faster than air. So don't forget to pump it up before your next ride.
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