A Guide to Inner Tubes
If you've had a puncture, you'll need to either repair your tyre's inner tube or buy a replacement.
The inner tube is the part of the tyre that contains the pressurised air which gives the tyre its structure and ability to absorb impacts. It's a secondary rubber structure that sits inside the tyre and inflates through a metal valve which sticks out through the inside of the wheel rim. Since it is protected from punctures by the tyre itself, the inner tube is relatively thin and malleable.
The most important thing to remember when buying a replacement tube is to make sure it fits! Tyres are sold in differing widths and diameters to fit different bikes and serve different purposes (See our guide to tyres here). Inner tubes are sold accordingly, marked with the width and diameter of the tyre they are designed to fit. This can be confusing, with tyres and tubes being marked up differently depending on the manufacturer and the type of tyre. In this guide, we'll walk you through the process of buying a new inner tube to make things a bit easier.
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How to Find Your Tyre Measurement
The first step is to look at your tyre to check its width and diameter. Many tyres have the same information displayed in several different ways according to different sizing standards within the cycling industry. The same tyre size could be referred to variously as: 23-622, 700x23c, or 28x? The last two are the most common, so we'll focus on those. The format for both of these sizes is the tyre's outside diameter followed by the tyre's width.
700x23c has the measurements in milimeters, so a 700x23c tyre has an outside diameter of 700mm and a width of 23mm. The letter at the end is a part of traditional French wheel/tyre sizing conventions - you'll also see wheels referred to as 700c or 650b. 28x? refers to the same measurements taken in inches: the outside diameter of the tyre is 28” and the width is ?”. You'll notice that 28" isn't exactly the same as 700mm, but it's rounded down for the sake of convention.
Generally speaking, milimeters are used for road and cyclocross tyres while inches are used for mountain bike and BMX tyres. The tyres on a hybrid bike could be measured either way since hybrids can take either road or mountain bike tyres.
How to Find the Right Size Inner Tube
Once you know your tyre measurement, you'll need an inner tube to match. Inner tubes are marked up according to the same conventions, with one important difference. Like tyres, inner tubes all have one set diameter and are marked accordingly as 700x... or 28x… . You’ll want to start by finding a tube with the same diameter as your tyre. The width, however, is marked differently because inner tubes are designed to fit tyres across a range of widths.
For example, you may see an inner tube marked 700x18-25c. This would fit all tyres with a 700c diameter and a width between 18mm and 25mm. Similarly, you might see a mountain bike inner tube listed as 29x2.1-2.35. That would fit any tyre with a 29” diameter and a width between 2.1” and 2.35”. This means that you can’t look for the inner tube that is marked exactly like your tyre. Instead, you look for a tube with a width range that includes your tyre. A 700x18-25c inner tube would be perfect for the 700x23c tyre pictured above.
Valves
The valve is the small metal tube to which you attach your pump to inflate the tube. Inner tubes come with either Presta or Schraeder valves. Schraeder valves are also known as car valves because they're the same type as found on car tyres. They are wider than Presta valves and most commonly found on mountain bikes, hybrids and kids’ bikes. Presta valves are prefers for road bikes and performance mountain bikes. Many road wheels are designed only for use with Presta valves and wider Scraeder valves won't fit. Many Presta valves are threaded on the outside and come with a small metal nut attached. This nut is designed to hold the thread in place in the rim, preventing damage during pumping and rattling while you ride.
If you are using wheels with deep-section aerodynamic rims, you will also need to ensure that the valve on your new tube is long enough. The valve needs to be long enough to fit all the way through the rim with enough room on the end for a pump to fit on securely. For example, 30mm deep rims generally require tubes with at least 45mm long valves. To make sure you get the right sized valves, simply check the valve length on your old tubes before throwing them away and make sure your new tubes have valves at least as long as your old ones. The valves can’t really to be too big, but excessively large valves will have a marginal negative effect on weight and aerodynamic drag. They also look a bit silly!
Some Presta valves are also fitted with removable cores. These removable cores allow you to fit valve extenders so you can use tubes with short valves on deep section wheels. Removable cores also allow you to fill inner tubes with tire sealant to automatically fix punctures should they happen.
Slime Self-healing Inner Tubes
Slime-branded inner tubes are pre-filled with a sealant liquid. As soon as a puncture is inflicted on the tube, this liquid is forced into the hole by the inner tube's air pressure, automatically sealing the puncture and preventing the loss of air pressure. This allows you to keep riding along instead of wasting time at the side of the road repairing the puncture yourself. They're great for urban riders who don't want to worry about carrying a repair kit around, commuters who don't want a puncture making them late for work or any cyclist who is sick of their rides getting interrupted. Racers might not be as interested because this sealant does mean extra weight. But it’s hard to win a race on a flat tyre too!
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