Bike inner tubes: tube sizes, valve types and marerials explained
You’re almost certain to have one in each tyre, but what should you look out for when it comes to your inner tubes?
It’s one of those bits of cycling equipment that looks simple and standardised. But there are a myriad of complications. Cycling Weekly guides you through the intricacies of the inner tube.
Inner tube sizes explained
First up is the tube’s diameter. Most road bikes will have 700c wheels and need 700c tubes to fit. But there are other sizes in use: some gravel bikes like the Cannondale Slate come with 650b wheels. It’s also the size used on smaller sizes of Canyon’s women’s range. You’ll need 650b tubes to fit these bikes.
Next is the tube’s width. Most 700c tubes come to fit tyres up to 25mm, which are most commonly fitted to road bikes. But you can also find wider tubes to fit the 28mm tyres that some bikes now come with. Cyclocross and gravel bikes and some city and hybrid bikes with 700c wheels will have even wider tyres and may need a wider tube still.
A tube for a narrower tyre will usually fit these wider tyres; it will just be a bit more stretched out to fill the space. It’s unlikely to burst, but if you get a flat it may go down more quickly. On the other hand, a wider tube may be awkward to get into a 23mm or 25mm tyre.
Mountain bike tyre sizes are usually stated in inches. So a 29 inch MTB tube will have the same diameter as a 700c road wheel, while a 27.5 inch tube will be the same diameter as a 650b road wheel. You can also get 26 inch MTB tubes. But since MTB tyres are typically wider than road tyres, they may be too wide to fit, even in a cyclocross tyre.
Inner tube valve types: Presta or Schrader?
Presta valve inner tube
Most bikes come with wheels that use presta valved tubes. These valves are quite narrow and have a screw at their valve tip. You need to unscrew it to get air into the tyre. Although the tyre will stay inflated with the screw loose, it’s a good idea to close it up so that you don’t accidentally let air out of your tyre. And a valve cap will stop muck getting into it when riding.
Some presta valves come in one piece, while others have cores that unscrew from the valve body. You can often unscrew them by hand or by wrapping them in a piece of old cloth or rubber and delicately using a pair of pliers. There are also core removal tools available.
A removable core can be replaced if it gets damaged – the screw part can often end up bent. The disadvantage is that you can unscrew the core by accident when removing a screw-on pump, undoing all your hard work pumping the tyre up.
Schrader valve inner tube
Some tubes have Schrader valves like those used on car tyres. These won’t fit into a wheel drilled for a presta valve. Likewise, if your wheel has a valve hole the right diameter for a Schrader valve, a presta valve will not fit securely and there’s a risk the tube will get pinched in the valve hole and blow out.
Woods valve inner tube
More of a rarity is the Woods valve. This looks like a presta valve, but has a collar holding the valve core in place. Not all modern pumps will fit onto a Woods valve because of the collar.
Valve length and valve extenders
Finally, keep an eye on the valve length. If you’ve got deep section wheels, you’ll need a longer valve to make sure that it protrudes through the rim. Some valves can be as long as 8cm. And you don’t want to get a flat out riding and find that your spare tube’s valve isn’t long enough to attach a pump – believe us, we’ve been there.
If your valve is still not long enough for your deep section wheel, you can buy valve extenders. These screw onto the valve and can add enough extra length to fit the deepest aero wheels.
Inner tube material
The majority of inner tubes will be made of butyl rubber. It’s the least expensive material and also the most robust. A butyl tube will be black and is repairable with a standard puncture kit if you get a flat.
Inner tube manufacturers often also have lighter weight butyl tubes in their line-ups. These are just made of thinner rubber. The weight saving comes at the expense of a bit more fragility though, so you need to be a bit more careful not to pinch a lightweight tube when fitting it. They are also likely to be more prone to punctures.
Finally, there are latex tubes. These are the lightest option and also roll faster than butyl. But they are even more fragile than lightweight butyl tubes and harder to fit. And they leak air more quickly than a butyl tube, so you need to reinflate them before each ride. They can’t usually be repaired if they do get a flat either. Read our test of latex tubes here.
Also be careful using latex tubes in rim braked carbon clincher wheels. Because carbon rims don’t transmit heat as quickly as alloy ones, prolonged braking on descents can lead to hot spots on the rim, which in turn can damage the tube leading to failure.
If you don’t drag your brakes on a descent this is unlikely to be a problem, but if you’re an inexperienced descender it’s something to be aware of.
Although they’ve been around for a while for mountain bikes, tubeless tyres are just starting to be used on road bikes. To run tubeless, you need a tubeless ready wheel and tyre. Don’t try to set up tubeless if you don’t have both of these, as you risk the tyre blowing out when riding.
Tubeless tyres use a separate presta valve that screws into the rim and has a rubber end to make a seal. Having put the valve in the rim, you mount the tubeless tyre. This has a tighter bead than a normal tyre, so it can be hard work to get it onto the rim.
Getting an airtight seal to the rim can also be tricky. You need to add sealant to the tyre. This helps with getting the tyre airtight and usually deals with small punctures when out riding.
But it may not seal a larger hole successfully, so it’s a good idea to still carry a spare tube, tyre levers and a pump just in case of a major leak.
Sealant tends to dry out over time, so you may need to top up. This is where the removable valve core comes in. Most sealants come with a nozzle to let you squirt sealant through the valve once the core has been removed.
There’s also the option of solid rubber tyres, which will rid you of inner tube problems for ever.
Puncture proofing an inner tube
If your tube has a removable core, you can get additional puncture protection by adding sealant to it. You take out the core, add around 25 to 30ml of sealant and refit the core. Again, this may not deal with the largest holes, but may help keep you going. While if you do flat, the sealant may stop a patch from adhering to the tube.
Watch out if you have latex tubes though, as some sealants can degrade the latex over time, causing it to fail. This can also be a problem with tubular tyres too, where the tube sewn into the tyre is often thin and made of latex.
Finally, you can buy inner tubes already filled with sealant, for an easy way to get some additional puncture protection.