Flat tyre on your bike: fix it yourself or take it in

A flat tyre is the most common problem on any bike, and also the easiest one to fix yourself. With three tools and twenty minutes, it is sorted almost every time. The important part is not just swapping the tube but finding what caused it. Otherwise you will be flat again in two days.

First: is it really a puncture?

A tyre that loses air slowly is not always punctured.

• Pump it up and wait. If it goes soft overnight, there is a hole or a valve that does not seal. All tubes lose a little air over time, so a tyre that took weeks to go down is not necessarily punctured.
• Check the valve. Put a little spit or soapy water on the tip. If it bubbles, the problem may be there.
• Look at the tyre. Turn the wheel slowly and look for glass, thorns or cuts.

Which valve does your bike have?

Before buying a tube or using a pump, look at the valve:

• Schrader: the same as on a car. Thick, with a pin in the middle. Common on city bikes, kids’ bikes and many mountain bikes. You can pump it at a petrol station.
• Presta: thinner, with a small nut on the tip that you unscrew before pumping. Common on road, gravel and many mountain bikes.
• Dunlop: found on some Dutch style city bikes. Less common.

Many pumps have a head for both Presta and Schrader. If yours does not, small adapters exist that fit in your pocket.

Which tube size you need

The size is printed on the side of the tyre. It may be in inches (for example 28 x 1.75) or in millimetres, such as 700x28c or the 28-622 format, where the first number is the width and the second the rim diameter. Tubes cover a range of widths, so pick one that includes your tyre’s width and has the right valve, and check the valve length if your rims are deep.

How to fix a puncture on a bike with inner tubes

What you need: plastic tyre levers (two or three), a new tube or a patch kit, and a pump that fits your valve.

1. Take the wheel off. If it is the rear one, shift to the smallest sprocket first: putting it back will be easier. Open the brake if it is a rim brake and the tyre will not pass.
2. Let all the air out and push the valve up into the tyre.
3. Hook one lever under the tyre bead, away from the valve, and clip it to a spoke. Put the second one in a hand’s width away and slide it round until one side of the tyre is off.
4. Pull out the tube.
5. Find the cause. This is the step that matters. Run your fingers carefully around the inside of the tyre, slowly, because if there is glass stuck in it you can cut yourself. Look at the outside too. If you pump up the old tube and find the hole, hold it next to the tyre: the position of the hole tells you where to look.
6. Check the rim tape, the strip that covers the spoke holes inside the rim. If it has moved or torn, the edge of a spoke hole can puncture the tube from the inside.
7. Put a little air in the new tube so it holds its shape, fit the valve through its hole and tuck the tube inside the tyre.
8. Fit the tyre back by hand, starting at the valve. The last section is hard: pinch the tyre towards the centre of the rim all the way round to gain some slack. Try not to use levers to close it, because it is easy to pinch the tube.
9. Check that the tube is not poking out anywhere between tyre and rim.
10. Pump to the pressure printed on the side of the tyre, which usually comes as a minimum and maximum range.

Patch or new tube? A well applied patch holds, and on a ride it is the practical option if you have no spare. But a hole next to the valve or a long cut cannot be patched: that needs a new tube.

If your bike is tubeless

Tubeless wheels have no inner tube: the tyre seals directly against the rim and has liquid sealant inside.

• Small holes are usually sealed by the sealant itself. Spin the wheel so the sealant reaches the hole and pump it up again.
• For a bigger hole, use plugs: a strip you push into the hole with a special tool.
• If none of that works, you can fit a normal inner tube as an emergency fix, removing the tubeless valve first.
• Sealant dries out over time. If you have not checked it for months, it may no longer seal.

Why you get more flats in the city

Streets are full of things that puncture tyres, and some causes come up again and again:

• Glass, especially at the edge of the road and in bike lanes, where there are no cars to push it aside. If you hear a crunch as you ride over something, stop and check the tyre.
• Thorns and spikes on dirt paths and in parks.
• Kerbs and potholes with low pressure. When you hit a kerb or pothole with a soft tyre, the tube gets pinched against the rim and you get two small parallel holes. This is known as a “snakebite”. The fix is riding at the right pressure.
• Worn tyres. When the rubber is very thin or you can see the threads, anything gets through.
• Something still stuck in the tyre. If you change the tube and get another flat straight away, the glass or wire is almost certainly still inside.

How to get fewer flats

• Check your pressure every week or two. It is the single most useful habit, and a floor pump with a gauge is cheap and lasts for years.
• Glance at your tyres now and then and pick out small bits of glass before they work their way in.
• Replace tyres when they are worn or cracked on the sides.
• If you ride a lot in the city, ask about puncture resistant tyres, or about going tubeless if your rims allow it.
• Always carry tyre levers, a tube or patches and a small pump.

When to take it to a workshop

Fixing a flat yourself is normal, but sometimes it is worth having a mechanic look at it:

• Rear wheel with an internal gear hub or a motor (many e-bikes): taking it off and refitting it involves more steps, and it is easy to leave something badly adjusted.
• Repeated flats with no clear cause. It could be the rim tape, a spoke end sticking out, a damaged rim or a tyre with a cut you cannot see.
• A cut in the tyre sidewall. The tube pushes out through it and it cannot be repaired: the tyre needs replacing.
• Tubeless that will not seal or that loses air at the rim edge.
• A dented rim or a wheel that no longer spins straight.
• No tools and no time, which is a perfectly good reason too.

If any of these sound familiar, or you would rather have it done properly once, on madridbikes.com you tell us what is happening with the wheel, in English or Spanish, and we assign a partner workshop in your area.