How Many CO2 Cartridges To Fill A Bike Tire (This Is My Rule Of Thumb)

CO2 cartridges (and bike tires) come in a range of different sizes and it can be hard to work out how many cartridges you’ll need to inflate your specific bike tires. If you’re trying to figure out what quantity you’ll need, then I’m here to help. I’ve tested out a range of cartridges with all the major tire sizes and I’ve got my guide below to how many are required to pump up each tire.

I’ve also got a brief guide to choosing a CO2 tire inflator (there are a few important factors to consider when you’re picking one).

Why I love CO2 tire inflators

For on-the-road repairs I absolutely love CO2 inflators.

Back home, I have a high-volume floor pump that inflates my tires quickly and easily. It’s great, but it’s not the kind of portable kit that you can easily strap on to your bike.

On bike rides I used to take a mini bike pump. These certainly work, but they’re also hard work, taking a lot of arm power to blow up your bike tube.

Nowadays I’ve almost totally switched over to taking CO2 inflators on my bike rides. They’re much smaller than a standard bike pump and they inflate inner tubes in seconds, with no hard work whatsoever.

(Side note – there is one situation where a mini bike pump is still my preferred choice – that’s for longer multi-day bikepacking or touring rides. For trips like that it’s easy to get multiple punctures and your supply of CO2 cartridges would disappear fast, leaving you stranded.)

But how many cartridges do you need for your particular tires? Well, here’s a handy reference guide I’ve compiled.

This is based on my actual tests and assumes that you’ll lose some gas as you fill the tube. In the real world I also go with an N+1 formula for the number of cartridges I take out with me. Where ‘N’ is the number in the table below and ‘+1’ is the extra cartridge I take in case of a top-up being needed or suffering from a second flat. Cartridges are cheap and very small so I always feel this is a worthwhile investment.

My handy guide to CO2 cartridges per tire size

CO2 cartridges per tire size

Tire size

# of 16g CO2

700 x 23c

1

700 x 25c

1

700 x 28c

1

700 x 35c

1

700 x 40c

1-2

20" x 2.0"

1

20" x 2.4"

1

26" x 2.1"

1

26" x 2.4"

1-2

26" x 4.0"

2-4

26" x 5.0"

3-5

27.5" x 2.1"

1-2

27.5" x 2.4"

2

29" x 2.1"

2

29" x 2.4"

2

Notes:

  • I’ve based this on 16g cartridges as these are the most commonly available size
  • For some tires I’ve shown a range of cartridges, this is because there are occasions where you may want tires more or less inflated e.g. 26″x4.0″ fat bike tires should be firmer for pavement and softer for snow or sand
  • For those tires needing multiple cartridges (e.g. fat bike tires being used on pavement), it may be worth trading up to larger capacity 25g cartridges

How to choose a tire inflator

There are a few factors to consider when you’re choosing a tire inflator for your bike. It’s also worth shopping around as there are some good deals to be had – including inflators that come packaged with a couple starter cartridges and discount bundles of cartridges.

Valve compatibility

Most inner tubes have one of two types of valve either Presta or Schrader. Schrader are the same type as you get on car (auto) tires. Presta are longer, thinner and with a locking nut at the tip.

All the CO2 inflators I’ve seen in my travels work with both Presta and Schrader. However there’s always an exception that proves me wrong! So, it’s worth checking that the inflator you’re buying is either compatible with your tube valves or (even better) fits both valve types.

Cartridge compatibility

Cartridges come in a variety of volumes from 16g to 25g. These are different size containers and not all containers fit all CO2 inflators.

Inflators that consist of either just the head, or a head and a separate sleeve, will be compatible with any size of cartridge. However inflators with a fully enclosed sleeve body may only be compatible with specific size(s) of cartridge.

Normally this isn’t an issue. But, if you have large volume tires to fill (such as fat bike tires), then you’ll need to carry more cartridges. Also it will restrict the cartridges you can buy – with a 16g-only inflator you wouldn’t be able to take advantage of a sweet deal on 25g cartridges, for example.

Control

CO2 inflators have one of two methods of releasing the gas. One is a push-to-activate – press the inflator head against the inner tube valve and the carbon dioxide is blown out of the cartridge. The second type of inflator has some sort of trigger that releases the CO2.

Both work fine, but I prefer the inflators that have a trigger. These give finer control on the gas released (and therefore the pressure you can get in your tire). In my experience they also lead to less loss of gas, so you get more of the cartridge contents into the tube.

Comfort

This is a big one for me.

Converting CO2 from a liquid into a gas takes a lot of energy. This energy comes from the heat of the cartridge. What this means is that a full cartridge that starts at room temperature will rapidly become painfully cold as it expels the gas.

If you’ve got your fingers wrapped around the cartridge when that happens it can be quite a shock!

It’s important to think about this when you’re choosing an inflator as they come in two types. One is just the bare inflator head, whilst the other has either a sleeve (sometimes made of foam or leather) or a plastic tube.

The sleeved CO2 inflators are comfortable to use bare handed, but you’ll need to be wearing gloves in order to use the non-sleeved inflators.

Value for money

Whenever I buy a new razor I’m constantly being conned into buying a fancy new Gillette or Harry’s handle that has a heavily discounted price and a couple starter blades. Once those blades are used up it turns out the new refill blades cost a (very hairy) arm and a leg.

Thankfully, CO2 tire inflators are different. The inflators themselves only cost about 20 bucks and you can buy new cartridges from a range of sources for good prices.

When you’re buying your inflator it’s worth looking out for a model that comes with some starter cartridges – if flats are a rarity for you, then these may keep you on the road for a long time.

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