How to fix a bike puncture

Getting a puncture doesn’t have to mean that your ride is over. With a bit of effort and knowledge you can be back on the road in no time. If you want to learn how to fix a bike puncture, you have come to the right place. 

What can cause a puncture?

• Penetration by a sharp object through the tyre e.g. glass, thorns.

• Trapping the inner tube between the rim and the tyre. This is called a pinch puncture. It is sometimes referred to as a snakebite because the puncture forms two little holes. It either happens because the wheel has hit a big obstacle and the tyre is squashed against the rim, or because the tyre is underinflated so the rim and the tyre are forced together.

• The valve is rubbing against the valve hole in the rim because it is too wide and the valve doesn’t have a collar.

• Because the tyre is worn, objects that would normally be deflected puncture the tube.

• Not really a puncture, but the tube can go flat because the valve has failed.
• Inflating the tube without checking the seating of the tyre. The tube pushes past the tyre and rim, gets trapped and explodes.

• Faulty rim tape causing the spoke ends or spoke holes to penetrate the tube.

 Why do we mend a puncture?

• You’re unable to get a new inner tube. 
• Because it is cheaper than buying a new tube.
• Because it’s good for the environment. The tube can be reused instead of ending up in the landfill. 
• To get the satisfaction of doing an old skool skill.

How to fix a bike puncture– tools needed

• Pump – tool that puts air in the tube. It is fitted on to the valve. This is one of the first things you will need to use when learning how to fix a bike puncture. There are two fundamental types, hand pump and track pump. A hand pump is more portable, but a track pump makes tyre inflation to the correct pressure much easier. There are pumps on the market that are a mixture of the two and are called portable track pumps. A foldaway foot holds it steady, the handle flips out so your hand is in a natural flat position when you pump and the valve adapter is attached to a hose that either rests alongside the pump or folds inside. Although too cumbersome for a full-on weight weenie, it is the perfect pump for someone who is quite happy to fix a flat by the roadside but doesn’t look forward to wasting valuable cycling energy pumping 80 PSI into a tyre with something resembling a syringe. 

• Puncture repair kit – there are two types, vulcanising and glueless. A vulcanising patch needs to be applied with a rubber solution and it creates a strong bond between the patch and tube. Because the patch is flexible it will follow the shape of the tube as it is inflated and deflated. Once the tube of solution has been opened, it will dry out, so check an opened tube first and don’t assume it will be ok. Because glueless patches are pre-glued like plasters they are less messy and much quicker to use. However, because they’re not bonded to the tube and not flexible they can come off. 

How to fix a bike puncture

The first task is to find the puncture and decide if it can be repaired. If the hole has an unusual shape such as a star shape after a blowout, you are not going to be able to find a patch that will cover the hole and if it is very near to the valve then it will be impossible to fix.

Pump the tube and listen for air escaping. Keep inflating and eventually you should find the hole.

If it is very small, then you may have to resort to another method. Put the tube into a bowl of water and watch to see where a stream of bubbles escape. That is your hole. You will need to dry the inner tube thoroughly before attempting to repair it as the solution won’t stick to a wet tube.

Once you have found the hole, mark it with a ballpoint pen while the tube is inflated.

Have a look at the patch that you’re going to use and offer it up to the puncture.  

Put 4 lines in a cross with the hole at the centre. Make the lines quite long as this is going to indicate where the solution goes.

Deflate the tube.

Find the square of sandpaper in your kit.  You are going to use this to key the surface of the tube and remove the moulding skin. Rub the sandpaper a few times over the marked area. 

Now open the tube in your kit. Although this is going to stick the patch to the tube, it’s not glue. It’s a vulcanising solution. You need to apply to a large enough area to cover the whole of the patch and it needs to be thin.

When it is put onto the sanded inner tube it causes a chemical reaction that creates microscopic hooks as it dries. Because of this do not apply the patch until the solution is dry. This can take at least 5 minutes, depending on the conditions.  If it is cold or wet it might take longer.  

Once it is dry to the touch and has a kind of dull matt finish you can apply the patch.  The patch has foil on one side.  Underneath the patch has microscopic hooks that will attach to the prepared site on the tube and they will join together.

Remove the foil and push the patch onto the solution on the tube.  

You will see that the edge is thinner than the middle. This is called a feather edge. It makes the patch less likely to lift. Don’t pick the plastic layer from the outside of the patch. If you do so the patch will most likely come off. If you stretch the patch onto the tube, the plastic should break and you will be able to peel the patch off from the middle out.  If you can’t, then just leave the plastic in situ.  

Some kits have a piece of French chalk. This is supposed to stop excess solution from sticking to the tyre. If your kit includes chalk, use it, if not don’t go hunting it down as the solution in the kit that you are using doesn’t need it.

Your tube is now ready to use.  

You might want to inflate the tube to see if it has worked.  Don’t over inflate the tube outside of the tyre as the solution and patch haven’t “gone off” yet and the patch could lift off. 

If the tube is going into a tyre it can be inflated to the correct pressure straight away as the patch will be pushing against the inside of the tyre or rim tape. 

If you are refitting the tube, make sure that you check the tyre first for any debris that might be stuck inside and could cause another puncture.

How to fix a bike puncture if it didn’t work the first time

Fixing a punctured tube doesn’t always work and is why mechanics will normally use the fool proof method of fitting a new inner tube. Lack of success can be attributed to the following reasons:

• Badly spread solution. If the rubber solution isn’t spread over a large enough area, then there won’t be enough of it under the patch.  It is better to have it spread over an area larger than the patch.
• The solution hasn’t dried. Depending on conditions, the solution can take a good 15 minutes to dry.  It is important to wait until it is completely dry before applying the patch.
• Not keying the surface of the tube. Don’t miss out on this seemingly innocuous part of the process. The sandpaper removes the releasant sprayed between the tube and the mould that formed it. Not removing this skin with the sandpaper can result in the patch not sticking properly.
• The position of the hole.  There are often ridges and seams on parts of the tube.  If the hole is there, then you will need a good quality, thin and flexible patch to cover the ridges and to make sure that the whole patch is really pressed firmly, otherwise the air can escape.
• Not patching the hole. Sometimes, if the hole is very small and the pen marks have rubbed off, it is possible to miss the hole when patching the tube.

Removing a patch and starting again isn’t always possible as the solution and patch start “going off” straight away.  Sometimes the best thing to do is admit failure and treat yourself to a new tube.

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