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What size inner tube do I need?

Everything you need to know about inner tubes including sizes, valves and types

Joseph Delves
18 Nov 2022

No one likes getting a puncture, even less so when confronted with the struggle of devining which inner tube you need. Inner tube sizing can be baffling at first and there's no quicker way to invoke the wrath of your local bike shop than by asking for a 'regular size' tube – there's no such thing.

With never-ending combinations of widths, diameters, valve lengths and types, we've compiled a guide to help make sense of this confusion and get you back up and running in no time. 

Is there a 'standard' size inner tube? 

The short answer is no. The slightly longer answer is that there are some sizes that are much more common than others. For example, most road bikes will use the same size tube, and most mountain bikes will use one of two different sizes. But there are many variables and understanding what they mean can help get you out of a sticky situation. 

All of this assumes you are running inner tubes at all. Most road and gravel bikes still come set up with tubes by default and if you don't know what you have, it's highly likely to be inner tubes. However, higher end bikes sometimes arrive tubeless out of the box.

If you're not sure about your tyres, let the air out of one of one of them and push the bead inwards to pop it off. Then check if there's a tube inside.

Running tubeless and need to fix a puncture? Read our guide to plugging a tubeless tyre

What do the numbers on my tyre mean?

700 × 35c = common description; 35-622 = ETRTO number 

Either measured in inches or millimetres, most tyres are described by their nominal external diameter. However, as tyre sizes have changed over the decades, these numbers have lost much of their direct relation to the exact tyre or wheel measurements.

Put simply, for the common description:

  •  the first number is the wheel diameter and the second is the tyre width

For the ETRTO number: 

  • the first number is the tyre width and the second is the inner diameter of the inflated tube (no, they didn't make it easy for us!) 

Further complicating this is the fact that decimal and fractional descriptions are not interchangeable. Not only is 26×1.75in not the same width as 26×1 ¾in, it also represents a different internal circumference.

Then there’s marketing. Road wheels are normally described as 700c, whereas on mountain bikes this same size is called 29 inches. On-road, smaller tyres are 650b, whereas when they come with knobbly off-road treads they’re known as 27.5 inches.

ETRTO: For desperate measures

Photo: Matthew Loveridge

If you’re unsure which tube to buy the best thing to do is default to the ETRTO (European Tyre and Rim Technical Organisation) number.

This is an international standard designed to make tyre sizing consistent and clear. It's printed somewhere on every tyre – it'll be two digits and a dash followed by three digits.

Know these two numbers, along with your valve type, and any decent bike shop will be able to get you the right tube.

What type of valve do I need? 

Left = Presta valve, Right = Schrader valve

There are three main types of valve.

  • Presta is the most common and found on all road bikes, and most gravel bikes. They require the smallest hole in the rim, as they are the narrowest valve, and need the end to be unscrewed before they can be inflated.
  • Schrader valves are the same as most car and motorbike tyres. Larger in diameter, they require a bigger opening in rim than Presta valves. They are slightly sturdier, with no fragile end, so are typically found on mountain and hybrid bikes.
  • Woods (or Dunlop) alves have the same diameter valve as Schrader, but use a removable flange to secure the valve in place. These are all but obsolete now and are very unlikely to come on any new bike, so best not to worry about them. 

You'll need a different pump fitting for each type, though many pumps will be equipped for both Presta and Schrader valves.

Do inner tube valves come in different lengths? 

If you’ve got deep section, aerodynamic rims, you’ll need a longer valve so there's enough protruding from the rim to attach a pump to. 

There’s no standard as to how much longer a valve will need to be, but 60-80mm valves will work for more aero wheels. For comparison, a standard valve tends to be around 40mm.

If your rims are really, really deep you’ll need to get a valve extender. These little widgets screw onto the end of a normal valve to add extra length, but can be fiddly to use.

Do I need lightweight or latex inner tubes?

Most bog standard inner tubes you'll see are made of butyl rubber. Many brands, however, will also make a lightweight version that costs a little more and can save you a few grams. These will roll a little faster but are more puncture prone.

Even more expensive are latex tubes. They’re delicate, hard to repair, don’t like being left for long periods of time, and leak air more rapidly than rubber alternatives.

However, they are faster and lighter. If you already own racing tyres and want the faster possible combination, they might be an attractive addition to your set up. 

Can’t I just bung any old tube in?

If you are in a complete pinch and happen to have a random inner tube lying around in your backpack, it can be possible to make the wrong size inner tube work with your tyre – up to a point.

A Brompton inner tube is not going to work on your road bike and vice versa because, even if rubber stretches to some degree, it's not going to go that far. 

Trying to make the wrong size inner tube work is going to greatly increase the chance that the inner tube will burst, get pinched inside the tyre or simply not fit over the wheel. 

In addition, fitting a tube that is the wrong width will also pose problems. Too wide, and it will impede your tyre sitting correctly on the rim. Too narrow, and it will over-stretch and pop. Consider yourself duly warned. 

Some common diameters, their uses, and descriptions


Roadie: 700c
Mountain bike: 29in, 29er

A standard size for racing bikes, tourers, hybrids, gentler gravel bikes and many modern mountain bikes


Roadie: 650b
Mountain bike: 27in, 27.5in, 650b

Smaller size for diminutive road bikes, rougher gravel bikes, and manoeuvrable mountain bikes


Roadie: n/a
Mountain bike: 26in

Formerly the standard mountain bike standard. Now less common. Increasingly used on kids' bikes

ETRTO 507 mm

Roadie: n/a
Mountain bike/BMX: 24in

Smaller size for kids' bikes, mountain bike jump bikes, and BMX cruisers

ETRTO 406 mm

Roadie: n/a
Mountain bike/BMX: 20in

Standard size on BMX bikes. Used on folding and kids' bikes

ETRTO 349 mm

Roadie: n/a
Vintage and Folding: 16 x 1 ⅜in

Bromptons and small wheeled vintage bikes

ETRTO 305 mm

Roadie: n/a
Mountain Bike/Kids/Folding: 16in

Kids' bikes and folding bikes (not Bromptons)

Punctured? As long as the damage is minor, there's not good reason not to patch your tube. Read our guide to the best puncture repair kits

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