Fix a flat tyre
Replacing or patching an inner tube takes twenty minutes, with three tools that fit in a pocket. The most important part isn't the patch: it's finding what punctured the tyre, so you don't get another flat.
What you need
- Two or three tyre levers (plastic)
- A new inner tube of the right size, or a patch kit
- A pump that fits your valve
- A spanner, if the wheel has no quick release
Before you start
The tube size is printed on the tyre sidewall (for example 700x32C or 29x2.2): a tube covers a range of widths,
check that it includes yours. Also check the valve type, which must match the rim and your pump:
| Valve | How to spot it | To deflate |
|---|---|---|
| Presta (thin) | long and thin, with a small nut at the tip | unscrew the nut, then press it |
| Schrader (car) | like a car valve, wider | press the pin in the middle |
How the wheel works
The tyre (1) holds onto the rim (4) by its two beads (2), stiff edges that hook under the rim's lips. The inner tube (3) sits inside. At the bottom of the rim there is a centre well (5): when you push the beads into it, the tyre gains a few millimetres of slack. That's the whole secret to removing and refitting a tight tyre without forcing it.
Steps
1. Remove the wheel
For the rear wheel, first shift to the smallest sprocket: the wheel will come out more easily. With rim brakes, open the brake (lever on the caliper, or unhook the cable) to let the tyre through. Open the quick release or unscrew the axle, then take the wheel out.
2. Deflate it completely
Depending on the valve (see the table above), unscrew the nut and press, or press the centre pin. Squeeze the tyre all the way round to push out the remaining air.
3. Lever one side of the tyre off
Go round the wheel pushing both beads into the centre well of the rim: this gives you the slack you need. Opposite the valve, slide a tyre lever under the bead, pull it back to lift the bead out and hook it onto a spoke. Slide the second one in 10 cm further along, lever it, then run it along the rim: one whole side of the tyre comes off.
4. Take the tube out
Pull the tube out starting opposite the valve, then push the valve back through the rim. Leave the other side of the tyre on the rim. Note which way round the tube was fitted: it will help you find where the hole is on the tyre.
5. Find the cause
This is the most important step. Pump the tube up a little and look for the leak by ear, holding it near your cheek, or in a bowl of water (bubbles come out of the hole). Find the matching spot on the tyre, then:
- Run your fingers gently round the inside of the tyre, there and then all the way round: a thorn, a shard of glass or a bit of wire may still be stuck in it. Use a rag if you're worried about cutting yourself.
- Look at the outside of the tyre: a cut, or worn down to the casing?
- Check the rim tape: the strip over the spoke holes must cover every one of them.
- Two small parallel slits on the tube? That's a pinch flat: the tyre was underinflated and the tube got trapped against the rim on an impact.
6. Patch or replace
A new tube is quickest at the roadside. For a patch: lightly sand around the hole, apply the glue if the patches aren't self-adhesive, let it dry until it's no longer shiny (a few minutes), then apply the patch and press hard for a minute.
7. Refit the tube
Put just enough air in the tube for it to hold its shape: it will twist less. If the tyre has a rotation arrow, check it points the right way. Push the valve through its hole, straight, pointing at the hub, then tuck the tube into the tyre all the way round.
8. Refit the tyre, by hand
Start at the valve: push it slightly up into the tyre so the bead slips under it, then push the bead back into the rim with your thumbs, working along both sides at once. The last section, opposite the valve, is the hardest: push the beads you've already fitted into the centre well all the way round, and it then goes on by hand. If it still won't go, let a little air out of the tube.
9. Check, inflate, refit the wheel
Push the valve up into the tyre then pull it back: the tube must not be trapped under the bead. Go round both sides: no tube showing between the tyre and the rim. Inflate to the pressure printed on the sidewall (between the minimum and the maximum), checking that the moulded line near the bead stays the same distance from the rim all the way round. Refit the wheel and tighten the axle.
Check it's done right
- The wheel spins with no bump or "hop": the tyre is sitting evenly on the rim.
- The pressure holds until the next morning.
- The valve is straight, not crooked in its hole.
Common mistakes
- Not looking for the cause: the thorn left in the tyre punctures the new tube within a few kilometres.
- Pinching the tube when refitting, with a tyre lever or under the bead.
- Forgetting to close the rim brake.
- Riding underinflated: that's what causes pinch flats (the two small slits).
What next
Always keep a spare tube, two tyre levers and a small pump on the bike: the full list is in Getting started. Patch the punctured tube at home, in peace, and keep it as a spare. Check your pressure every week: a well-inflated tyre gets far fewer flats.
Sources
This guide was checked against the following documents:
- Park Tool, Tire and Tube Removal and Installation
- Trek, How to fix a flat
- Décathlon, inner tubes: repair and compatibility (in French)
Values vary between models: your part's manual always takes precedence.