Flat tyres: How to diagnose and fix the problem

Difficulty level : average

Reading time: 5 minutes

Bike tyres don’t last forever – sooner or later you’ll encounter the problem of a punctured tyre. When air is leaking out of your tyre, it’s important to locate the source of the leak quickly.

Has the leak just started, or has it been happening over time? Are your tyres often flat, even when you’ve just inflated them? Or do you notice air suddenly escaping from your tyre? Read on to learn how to identify the cause of the problem and fix it.

Have you hit a sharp object?

Bicycle tyres are commonly punctured by sharp objects on the ground, which can pierce the tread or the tube. Sharp thorns, metal and broken glass are often the culprits.

If the puncture is too big to repair, it’s best to change your tyre. If the puncture is smaller, you may want to fix the tube and save yourself from having to buy a replacement tube or tread.

Before attempting the repair, carefully check the tread and remove all sharp objects so that you can re-inflate the repaired tube smoothly.

To fix the tube, you’ll need a bucket of water, a bicycle pump, a repair kit and a felt-tip pen. Follow the steps below.

First, inflate the tube and immerse it in the water. Little bubbles will come up, showing you where the puncture is located.

Now, put your finger over the hole, take the tube out of the water and mark the location of the puncture with the felt-tip pen.

Sand down the area around the hole with the sandpaper from the repair kit.

Now you can apply the vulcanizing solution around the damaged area. The solution should be runny; very viscous or thick solutions are usually too old and should not be used. Apply a thin, even layer of the solution over the damaged area.

In your repair kit, you can usually find a patch. Press this patch firmly onto the hole and let it take effect for 4–5 minutes.

Now you can remove the plastic foil from the patch and inflate the tyre to check if the repair was successful.

Does the valve sit right?

Bike tubes are structured as follows: a small metal tube allows air into the tyre tube. In the metal tube there is a valve that prevents air from escaping.

If you notice air escaping from your tyre over time, resulting in a flat tyre, it could be that the valve has come loose due to the pressure in the tube. If the small bolt ring that holds the valve in the rim is even slightly loose, air will escape from the tyre. Therefore, these bolt rings should always be tightly fastened.

First, remove the valve cover from the valve.

You should see a small female screw; loosen it carefully. Now the valve is exposed.

If the tyre has too much air, all you have to do is press the pin on the top of the valve, which lets excess air escape.

Finally, fasten the valve and put the valve cover back on.

Is the tyre rubber leaking?

Repaired your tyre and checked the valve, but still finding it’s flat again after a few days? Then it may be that there’s still a sharp object in the rubber, which will continue damaging the tube until it’s removed.

Another possibility is that the outer tread has some serious holes or tears, so that the inner tube is no longer well protected. This means the tube is exposed in places, allowing small leaks, punctures, pierces or bursts.

Small, superficial tears in the outer tread are not necessarily a reason to immediately buy a new tyre. However, such tears tend to grow over time, depending on UV rays, your style of cycling, and the ground surface. If you detect deep grooves in the rubber of the tyre, you should get a new one to ensure the tube is optimally protected.

Issues with the rim or rim tape (liner)

You will detect issues with the rim when the brake surface is somewhat curved or arched inwards, due to wear. If the brake surface is less than 1 mm, it is time to get a new rim. But before you install a new tyre tube, make sure that the rim comes with compatible rim tape (also called a rim liner). This protects the tube from any damage from the rim itself.

Spoke heads or bore holes in the rim can inflict damage to the tube as well. And even displaced or worn rim liners can transport mud or dirt from the spokes via the rim to the tube, which can cause punctures.

Tubes that are not properly aligned on the rim – and thus on the rim liner – are also vulnerable to damage. Also make sure that the rim width matches the size of your bike tyre. The rim liner should be wider than the inner side of the rim itself by 2–4 mm.

Check your tyre pressure

Your bicycle tyres’ pressure should also be kept at an ideal level to minimise the chance of punctures in the tyres and the tubes.

Generally, tyre pressure requirements depend on the road surface, the kind of tyre and the type of bicycle. Wider tyres need less pressure than narrower ones. Learn more about how to inflate your bicycle tyres.