A CO2 inflator will fill an inner tube in seconds, saving you time and effort and allowing you to get back in the saddle as quickly as possible. Here's what to look for when you buy one.
CO2 inflators get your tyres up to pressure quickly — just the job when you're in a hurry to get moving again on a wet winter morning
A pressurised canister of carbon dioxide gas is pierced and the gas expands to fill your tyre
Cartridges can cost over £3 each, which makes this a pricey way to fix a flat; you'll want to save them for emergencies and shop around
We strongly advise you to carry a manual pump as well, just in case
There are two main parts of a CO2 inflator: the head and the replaceable CO2 cartridge (sometimes called a canister).
The head attaches to the valve stem and is the means by which the carbon dioxide is transferred from the cartridge to your inner tube.
The CO2 cartridge is a steel tank of pressurised gas that's easily small enough to stash in a saddle pack. The pressure means that once it's attached to the valve the CO2 inflator will fill your inner tube/tyre in a fraction of the time it would take with a mini pump or even a floor pump.
Most CO2 inflators that we've reviewed lately take threaded cartridges – the neck of the cartridge screws into place on the head, the seal at the top getting pierced in the process.
Other CO2 inflators take non-threaded cartridges that push into place on the head.
Threaded cartridges usually cost just a little more than non-threaded cartridges.
Some inflators, such as the Genuine Innovations Ultraflate that we reviewed (£19.99), work with both threaded and non-threaded cartridges, but most are compatible with one or the other.
Inflators for threaded cartridges can be minimalist, head-only designs that weigh very little and take up just hardly any room. If you really want to save space, this is the better option for you.
Inflators for non-threaded cartridges need some form of body to hold the cartridge in place, so they tend to be larger and weigh a little more – although the hollow shell that the cartridge sits in is never particularly heavy. The body also protects your hands from the freezing cold cartridge in operation (see below).
CO2 cartridges come in various sizes starting at 12g. A 16g cartridge will fill most road bike tyres but you'll need a larger cartridge for some mountain bike tyres, depending on the volume and the pressure you like to run.
If you want to be safe, you can carry a couple of cartridges. If you want to be really safe, you can carry a mini pump or a combined CO2 inflator and mini pump like Bontrager's Air Rush Road Mini Pump (£24).
With some basic CO2 inflators, the gas flows through the head as soon as the top of the CO2 cartridge is pierced. This means you need to have the head already in place on the valve or you'll waste the gas.
Most CO2 inflators have some means of stopping/controlling the flow: you either push the head on to the valve to inflate, twist a wheel, or use some form of trigger.
As well as being easier to operate, these inflators have the advantage of allowing you to use half a cartridge of CO2 to top up a tyre, and saving the rest for another time.
Some CO2 inflators are easier to use than others. They're all pretty small and some are downright fiddly, especially if your fingers are cold and wet after replacing an inner tube on a winter ride, so choose something that's simple to operate.
It's definitely worth trying out a new CO2 inflator at home to get familiar with the way it works rather than waiting until you puncture out on the road. You'll have to sacrifice a CO2 cartridge but that's better than finding yourself stuck in the middle of nowhere because you accidentally lost a load of gas.
A CO2 cartridge gets cold when you let the gas out – really cold! If you simply held a bare cartridge in your hand while inflating your tyre it would be extremely uncomfortable, your skin could stick to the metal and you might do yourself some damage.
Some inflators hold the cartridge within a plastic body so this isn't an issue. With others, though, you'll need to protect your hands in another way. Full finger gloves will prevent freeze burns, but you're unlikely to be wearing them in the summer so carry something like a neoprene cartridge sleeve.
The UK Civil Aviation Authority (CAA) says that you can carry "no more than four small cylinders of carbon dioxide or other suitable non-flammable non-toxic gas per person and the water capacity of each cylinder must not exceed 50ml".
For CO2, a gas cylinder with a water capacity of 50ml is equivalent to a 28g cartridge.
However, Gatwick Airport's security advice says, "There are some items that you’re not allowed to take on your aircraft in either your hand baggage or your hold luggage [including] any gas cylinders."
The US Transportation Security Administration (TSA) says, "Except for personal medical oxygen cylinders, you can only carry an EMPTY compressed gas cylinder onboard a plane."
If you take CO2 cartridges on a flight, be prepared to lose them. Our advice would be to have a back-up pump if you're flying.
A CO2 inflator will provide the blast you need to seat a tubeless tyre on a rim but it'll have a detrimental effect on some sealants. Check what your sealant manufacturer has to say before going down this route.
Pros of CO2 inflators
• Quick and easy to use
• Small and lightweight
Cons of CO2 inflators
• You could find yourself stranded if the gas runs out
• You're tied in to buying replacement cartridges
The Pro Bike Tool CO2 Inflator is a neatly machined, fully controllable way to blast your tyres, just make sure that the snug valve union doesn't remove your valve core afterwards.
The knurled sections of the head give excellent grip, the foam sleeve fits tightly enough that you can screw the cartridge in with it on, and the easily replaceable o-rings don't leak. It fits both Presta and Schrader valves without modification.
The valve gives easy and progressive control over gas flow, which can help when seating awkward beads or if you find yourself without hand protection.
Lezyne's Control Drive provides easy control of the flow of gas, which makes it really easy to get any Presta or Schrader inner tube fully inflated.
The Control Drive is a simple, compact design that works effectively. You simply push it on to the valve, and turn the inflator head to release air. The knurled ring provides good grip and there's a little graphic on the end of the head that tells you which way you need to turn it. You can open it a little for a small release of gas, or open it fully to get the full beans.
A neoprene sleeve fits over the CO2 cartridge to protect your hands during use.
The Muc-Off Inflator Kit allows you to inflate your tyres quickly and get back to riding in no time. The chuck works really well, inspiring confidence that it won't release CO2 while attaching, there's a button that lets you control the release of gas, and a neoprene sleeve to stop you freeze-burning your fingers
In the kit you get two 16g road cartridges (there's a mountain bike version of the kit with 25g cartridges), one CNC-machined inflator head, and the neoprene sleeve.
The head is a tidy piece of kit that's CNC-machined from aluminium alloy. It is threaded and can be screwed onto either a Presta or Schrader valve, which is much more confidence-inspiring than push-fit alternatives.
Birzman's Roar Control is similar to many others on the market but it does offer one neat touch over some of the cheaper models: you can control the flow by twisting the CO2 cartridge.
Once you've screwed the threaded cartridge on to the head to puncture the seal, you just unscrew it slowly and the gas is able to flow. The flow rate depends on how far you unscrew it, so you can just let the CO2 trickle out until you're sure everything is seated right, then blast the tyre up to pressure.
Birzman provides a neoprene sleeve to slide over the cartridge to prevent freeze burns.
The head is CNC-machined from aluminium alloy, and it's threaded to enable it to be screwed onto either a Presta or Schrader valve.
The Genuine Innovations Ultraflate CO2 inflator is a super-useful bit of kit, although it is larger and heavier (155g) than many rivals.
The unit, made of tough glass nylon and featuring brass parts that won't rust, comes in two parts: a cartridge holder and a head unit – which features a trigger and lock switch to control and secure the flow.
This inflator takes non-threaded 20g cartridges as well as threaded 16g and 20g cartridges. They all work equally well so it doesn't matter which you pick up as spares. It works with both Schrader and Presta valves,
The trigger means you can ease the delivery, and the holder keeps your hands safe from freeze burns.
Once done, if there is any gas left you can lock the trigger and use it next time.
This combined mini pump and CO2 inflator makes it very easy to get wide tyres on endurance, all-road, cyclo-cross and gravel bikes up to pressure. It is solidly made with the CO2 inflator integrated into the head.
To use the pump, you extend the head to reveal a short flexible hose, remove the CO2 head, and use the knurled nut to lock onto a Presta valve, then pump away.
If you want to use the integrated CO2 inflator, you simply twist the head off the pump and it screws directly onto a cartridge. It's that simple. You can regulate the flow of gas as you need to, and save any remainder for the rest of the ride.
The Bontrager Air Rush Road CO2 Pump is a nifty little dual design that won't leave you deflated on the roadside.
The pump on its own is a very capable little design. It is small so it can only shift so much air, but the upside is that it's easy to carry in a jersey pocket, independent of the CO2 canisters and mounting bracket.
The pump also acts as the regulator for the CO2 cartridge. The head has two sides, with one being a threaded aluminium adaptor for the cartridge. The adaptor is well made and the cartridges thread easily.
The inclusion of a cartridge insulator is really useful for protecting your hands from the super-cold canisters. It's a simple rubber sleeve but it's a nice touch.
As far as we can tell, these are the cheapest 16g cartridges that you can buy individually. Of course, you'd be mad to do that as you'd pay another £7 for delivery, but if you're ordering something bigger they're a handy add-on.
Alternatively, here's a source of packs of 30 for £18 plus £4 shipping.
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Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now pushing 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.