Your bike’s inner tube is an inflatable tube made of synthetic rubber which sits inside the tyre and makes it airtight. Most bike wheels – road, city bike, MTB etc. – still use inner tubes to hold the air, although in recent years car-style ‘tubeless’ tyres have grown in popularity.
Your inner tubes are one of those things on the bike that you are never aware of until things go wrong – i.e. you have a puncture that has gone through the tyre and pierced the tube. If this happens, your inner tube can be patched using a puncture repair kit, but if the hole is too big (or you can’t be bothered, let’s face it), you’ll have to get a new tube.
There are two things to bear in mind when replacing a tube:
1. Wheel size: This will differ between bike types – generally there are a limited number of standard sizes between road and MTB bikes but there can also be deviations in width and volume etc. 2. Valve type: The tube is inflated via a valve which fits through a hole in the rim of the wheel – there are a few different types of valves so when replacing a tube it’s important to ensure you have the right one, or it may not fit through the rim hole.