The trouble with tubes

We’d like to welcome back our family bike guy this week as he takes a novice’s look at inner tubes and attempts to shed a little light on this often confusing accessory. 

Bicycle Inner Tubes.

If you own a bike, you will have suffered from a flat tyre I’m sure. If you live in a household with more than one sort of bike, chances are you’ll have been faced with challenge of figuring out what inner tube is needed for each bike. You might have, for example a kid’s 20″, a BMX, a hybrid city bike, a road bike and 29″ mountain bike. This garage full would require five completely different and totally incompatible inner tubes. So where do you start? What are the different sizes? Why do some appear in metric sizes and others in imperial? And what the heck is the difference between a Presta and Schrader valve anyway?

Inner tubes and tires are confusing. If you only own one bike, then once you know what inner tube size and valve you need all you have to do is choose a brand or price point. I, like many folks live in a house with more than one type of bike and that’s were it can start to get a bit tricky.

Let’s start with the basics.

An inner tube is the inflatable doughnut that fits inside the tyre, giving it structure. The inner tube itself has no structure. It’s only real requirement of an inner tube is that is does not leak.

But you knew that right? Good, lets move on.

If you walk into the Cycle Centre and ask for an inner tube one of the first questions you might be asked is “what valve type?”

There are two main types of valve, the Presta and the Schrader (there is a third much less common valve known as the Dunlop or Woods valve).

Presta valve stem

Unusually tall Schrader valve stem with valve core

Unusually tall Schrader valve stem with valve core (Photo credit: Wikipedia)

Now, I used to get confused with the two types. Always. The way I remember now is this:-

The Presta valve has a small nut at the end that once unscrewed slightly is “pressed” to release air. Press = Presta.

The Schrader valve is basically the same as the one you’ll see on your car’s tyres.

The Presta valve is the norm on road bikes and hybrids. Schrader valves are still popular on BMXes and mountain bikes. The Presta valves also come in different lengths, just to add to the confusion. The longer valves are for pricey road road bikes with deep rims. Presta valves are also thinner, so you may be able to buy a Schrader inner tube in the same size but it won’t fit through the hole in your rim.

Now, the next question you’ll be asked is “what size?” and this is normally when the problems start.

Basically every inner tube has two measurements. One is related to the diameter of the wheel rim and the other to the width of the rim.

Road bikes and hybrids are generally measured in millimetres and mountain bikes, 29ers and BMXes are usually measured in inches. The easiest thing to do is look for these dimensions on the inner tube you are looking to replace. They’ll appear as:

700×28 or 26×2.0 – the larger number is the diameter and the smaller the width.

If you don’t have the inner tube anymore, check the tyre wall for the same measurements.

If you have a rim but no tyre (and the dimensions of the rim aren’t marked on it) you can take a measurement across the axle from rim edge to rim edge. Confusingly, this dimension might not be the actual size of tube you need but it will be close enough to help. The ideal would be to bring the wheel into the Cycle Centre for them to size for you. Failing that, they are pretty good at working it out from the type of bike you ride. The main area of confusion is around hybrid bikes with 700c wheels and 29er mountain bikes, with 29″ wheels. The two dimensions are actually so similar the inner tubes are interchangeable in terms of diameter. However, the hybrid bikes normally only have 28 or 32mm tyres on and a 29er will have 2″ or more tyres. So whilst the tubes for these tyres will fit around each others rims, the 29er tube once inflated will push the hybrid tyre off it’s rim and the hybrid tube would not properly inflate the 2″ 29er tyre.

Believe it or not, inner tubes are relatively simple when compared to selecting a tyre. But I’m not going into that right now.

To recap: When you need a new inner tube, you should know –

  1. the type of valve,
  2. the diameter of the wheel/tyre
  3. the width of the rim/tyre

Assuming you’re still awake and would like to read more on tyre and tube sizing then take a look at this extremely detailed guide:

Tyre Sizing Systems