BIKE COMPONENTS AND ACCESSORIES: The right inner tube for your mountain bike

The classic bicycle inner tube is still made of butyl rubber, is very airtight and elastic and therefore covers several tyre sizes in principle. A standard Schwalbe inner tube, such as number 19, for example, therefore fits both 27.5 x 2.35 inch and 29 x 2.25 inch tyres.

Nevertheless, it is advisable to choose an MTB inner tube that matches the rim and tyre size. Although a 26-inch inner tube will also fit a 29er tyre in an emergency, the strong stretch increases the susceptibility to punctures. Conversely, an inner tube that is too large can form creases during fitting or even be squeezed between the rim and tyre. In addition to the sizes, most manufacturers also offer different weight classes with different wall thicknesses. Lightweight inner tubes (approx. 100 to 150 grams) with a wall thickness of just 0.45 millimetres reduce rolling resistance, but increase the risk of punctures and need to be pumped up more often. They are therefore more suitable for cross-country use. Particularly strong downhill tubes provide effective protection against punctures, but roll very slowly. The manufacturers' standard models weigh around 160 to 220 grams and offer a good compromise between the two worlds. The most important data can be found both on the packaging and on the inner tube itself.

Good packaging provides information about all the important data: Size in inches and ETRTO, valve type and, in the best case, length. Wall thickness and weight will only be given in exceptional cases. At least the size information can also be found on the inner tube itself.

Take care with high profile rims: If the valve is too short, the pump head cannot be fitted properly and does not close airtight when pumping.

The valve must fit the rim bore. If Sclaverand valves are used in rim bores that are too large, this can lead to the valve tearing off. There are no differences in air retention between the valves.

Number crunching: How to find the right size

The tyre size is designated according to the European tyre and rim standard ETRTO (European Tire and Rim Technical Organisation). For example: ETRTO 57-622 indicates the width (57 mm) and the inner diameter (622 mm) of the tyre in millimetres. The inch designation only indicates the approximate outer diameter and tyre width. 29 x 2.25 inch corresponds to the above example.

The 3 most important mountain bike sizes at a glance

• 559 = 26 inch
• 584 = 27.5 inch
• 622 = 29 inch

Interesting facts about the valve

Valve types at a glance

In the mountain bike segment, the Sclaverand (also known as Presta or French) valve (1) and the Auto/Schrader valve (2) have established themselves. The classic Dunlop valve (3) and the Italian Regina valve (4) do not play a role. Advantage of the auto valve: You can simply fill the tube with air at the petrol station using the compressor.

Rim nut yes or no?

The rim nut is only used to lock the valve in place when pumping. An overtightened rim nut increases the risk of a valve tearing. If the tyre moves on the rim during braking, a valve without a nut can still tilt slightly. This may prevent the valve from tearing off.

The right valve length

A standard valve measures around 35 to 40 millimetres. This is too short for some high (carbon) rims. Sclaverand valves are therefore also available in a length of 60 millimetres for some models. Alternatively, a valve extension (1) helps when inflating. A valve spanner (2) can be useful when screwing the extension on and off.

Alternative materials for MTB inner tubes

Latex

Unlike rubber hoses, latex hoses are not vulcanised with the addition of sulphur under pressure and heat, but only dried at outside temperature. Latex hoses are extremely elastic and therefore roll more easily and offer good protection against punctures. However, they are not particularly airtight. They may need to be re-inflated before a ride. Currently only available from Michelin and in 26 inch tyres.

Plastic

Polyurethane is a high-quality, age-resistant plastic, but is less elastic than latex and butyl. Eclipse (1) uses it to create a hose weighing just 59 grams, which is also extremely puncture and puncture-resistant.

With the Evo Tube (2), Schwalbe has also developed a plastic inner tube. It is made from the thermoplastic Aerothan and is said to be airtight, puncture-proof and, at 68 grams, also very light. One detailed comparison test of MTB inner tubes can be found here.