At this time of the year you may well be getting more punctures than usual. This month I’m concentrating on tyres and tubes. Find out how to prevent slow punctures, select tyres and tubes of the right size and pack a spare inner tube for emergencies.
For tasks like tyre inspection or for removing wheels, it’s best to invert your bike. The easiest way to turn your bike over that I’ve found is to [A] lean over it and grab hold of the frame and forks as low as you can, [B] lift the bike letting it flip toward you, and [C] gently lower it to the ground. If your brake cables get trapped between the levers and the ground, placing a support under the bars is a good idea. To turn your bike the right way up again, grip frame and forks nice and low and flip the other way.
|[A] [B] [C] Turning your bike is easy providing you grab the frame low down|
|[D] A rash of tiny cracks like these is nothing to worry about|
Once your bike is inverted you can easily take a good look at the condition of the tyres. Try slowly spinning each wheel in turn, looking carefully at each sidewall in turn. This helps you to spot sidewall-irregularities, such as splits or tears. Many tyres develop a uniform rash of tiny surface ‘cracks’ in the rubber sidewalls [D], but these are shallow and perfectly OK. On the other hand, any isolated bulges or cuts to the sidewall are serious danger signs, especially if you can see the inner construction of the tyre, like the ‘cords’ which make up the casing. If you spot anything like this, fit a new tyre.
|[E] Dig out glass fragments from all cuts in the tread|
Check the tread too. Be on the lookout for any cuts containing slivers of glass or flint which, if left embedded in the tread, will work their way deeper until they eventually penetrate the inner tube, causing a slow puncture. Use a small screwdriver to gently probe for, and excavate, any foreign bodies you find [E]. Unlike the sidewalls, minor cuts in the tread are harmless providing they are free of glass. However, if the tread pattern is well worn, embedded bits of glass can more easily penetrate the tyre, especially if the tread is wet. If you are getting a lot of glass punctures, worn tread may be the reason and you should think about getting a new tyre.
|[F] These are the markings to make a note of|
So, what size replacement tyre do you need? First, write down the markings on the side of the tyre [F]. In particular, look for a group of two numbers separated by a dash, for example 28-622. This mark is the system of tyre sizing set by the International Organisation for Standardisation (ISO). The two digit number is the width of the tyre in millimetres. The three digit number is the diameter of the rim in millimetres, which is the important measurement when selecting replacement tyres. Generally, any tyres with the same three-digit number as the tyre you are replacing will fit your wheel. So, in the 28-622 example, get a replacement marked as xx-622. Narrower or wider tyres (like 25-622 or 32-622) will also fit your wheel providing that they have the ‘622’ marking. However, avoid choosing a tyre which has a very different width from your existing tyre as it can lead to other problems. (Sheldon Brown’s article gives more information about which width combinations work well.)
Carrying a spare inner tube on the road is a wise move, so you may want to get one too. Inner tubes are designed to fit a range of tyre sizes. Unfortunately, every inner tube manufacturer uses a different system for specifying which tyres their tubes fit! Don’t be surprised to see boxes of inner tubes bearing markings like 47-57×559 (26″x1.75″ to 2.125″) or 26×1�-1�” (37×590). Here, the ISO tyre sizes are given with the nominal sizes (like 26″x1.75″), together with a range of compatible tyre sizes. I find it’s best to concentrate on the ISO numbering: the first example means simply that the tube fits any tyres from 47-559 up to 57-559. To be completely sure, ask the sales assistant to confirm you’ve selected the correct inner tube before buying: then, if it doesn’t fit, you can more easily argue for a replacement.
It’s a bit frustrating to discover your spare tube has developed a puncture from six month’s of being shaken around in your pannier or rucksack. Here’s how I pack my spare inner tube into a neat bundle that stays in good condition until you need it. First, roll the tube tightly, starting opposite the valve [G]. Let any trapped air out as you go. Next, unroll the tube again, refit the dustcap on the valve (to stop it cutting into the tube), and start rolling the tube from the valve end [H]. When you have a tightly rolled tube with no air inside, use a rubber band to keep it together [I]. Finally, wrap the bundle in a couple of layers of kitchen wrap (‘cling film’) to protect it from any abrasion damage [J].
|[G] First roll the tube to squeeze trapped air out||[H] Finally roll from the valve end to make a tight bundle|
|[I] A rubber band keeps it together||[J] Cling film protects the spare tube|
Sheldon Brown’s excellent tyre-sizing article is at http://www.sheldonbrown.com/tire_sizing.html.