How to Fix a Flat

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Fixing a flat is a ten-minute job that people dread because the first time they did it, it took forty minutes and they did it again two miles later. Both of those problems have the same cause, and it’s a single step that gets skipped: you have to find out what made the hole before you put a new tube in.

The procedure below is Park Tool’s published method, quoted where it matters. The notes about what goes wrong are Stephen’s, from doing this at the side of a road in poor weather more times than he’d like — he’s not a mechanic, but this is a job you learn by getting it wrong in the cold.

Before anything: what to carry

None of what follows works if the kit is at home. The minimum is boring and non-negotiable: a spare tube, two tire levers, and a pump.Add a patch kit if you ride far — it’s your second flat, and it weighs nothing.

Park Tool’s position on tube-versus-patch at the roadside is worth internalising: “simply replacing the punctured inner tube with a new tube is always the safest and most reliable procedure”. Swap the tube at the road. Patch the punctured one at home, on a table, in the warm, where the glue can actually cure. Patching at the roadside is a skill you deploy when you’ve used your spare, not a first resort.

Check that your spare tube fits your valve holes and your rim depth.A tube with a 40mm valve stem on a 50mm deep rim is a tube you cannot inflate — the valve won’t protrude far enough for the pump head to grab. Stephen has made this exact mistake, at distance, with a perfectly good spare tube in his pocket. Check the tube you carry against the wheel you carry it on, once, at home.

The procedure

1. Get the wheel off and deflate completely

Rear wheel: shift onto the smallest cog first — it slackens the derailleur and makes the wheel drop out and go back in far more easily. Then open the brake or the quick release, and out it comes.

Then deflate it properly. Park Tool: “Deflate tire completely. Even a small amount of air left in the tube can make it more difficult to get the tire off.” This is the step that turns ten minutes into forty. If the tire is fighting you, there is almost certainly still air in it.

2. Break the bead and lever one side off

Before reaching for the levers, push the bead inward all the way round with your thumbs. The rim has a deeper channel in the middle, and dropping the bead into it buys you slack — sometimes enough to get the tire off without levers at all.

Then, per Park Tool: “Engage one tire lever under bead of tire. Engage second lever 1-2″ (25-50mm) from first lever then pull both levers toward spokes to lift bead off rim.” Note the spacing — 1 to 2 inches apart. Levers spread further apart than that are fighting the tire’s tension instead of using it, which is why the tire won’t come and why the lever snaps.

One side only. You never need the second bead off to change a tube, and taking it off doubles the work of putting it back.

3. Pull the tube out — and don’t lose track of where it sat

Push the valve up through the rim and draw the tube out. Keep it oriented. You are about to use the position of the hole in the tube to find the cause in the tire, and that only works if you know which part of the tube was sitting where.

4. The step everyone skips: find the cause

This is the actual guide. Everything else is mechanical.

Find the hole in the tube — inflate it slightly and listen, or run it past your lip, which is far more sensitive than fingers. Then read it:

• Two small holes side by side, on the rim side of the tube: a pinch flat. The rim squeezed the tube against an edge — you hit something hard at too low a pressure. Nothing is stuck in your tire. Fix the pressure, not the tire. This is the failure mode tubeless deletes entirely.
• One hole on the outside (the tread side): something went through the tire and is very possibly still in it. Go and find it.
• A hole on the rim side, on its own: suspect the rim tape. If the tape has shifted and exposed a spoke hole, the tube is being pushed into a hole by its own pressure, and no new tube will survive it either.
• A split around the valve base: usually the tube was installed with the valve at an angle or ridden badly under-inflated. Fit the new one carefully and straight.

Then inspect the tire, in Park Tool’s words: “Visually inspect inside of tire casing for nails, glass or debris. Wipe inside of casing with a rag, and then carefully feel inside with fingers.” Go all the way round. Use the hole in the tube to know where to look hardest.

Stephen’s note:do this carefully — a shard of glass will slice a fingertip as happily as it sliced the tube. Go slowly, with light pressure. And do it even when you’re cold and it’s raining and you just want to be riding, because the alternative is doing the whole job again in ten minutes with your last tube already used. He has learned this the expensive way, which is walking.

5. Fit the new tube

1. Put a little air in it first. Park Tool: “Inflate tube enough for tube to just hold its shape.”This is the single best trick in the job. A tube with a breath of air in it holds a round shape, sits where you put it, and is dramatically harder to trap under the bead. A flat tube is a flat ribbon that folds and hides exactly where you’re about to lever.
2. Valve first, straight through the hole. Push it up perpendicular to the rim, not at an angle.
3. Feed the rest of the tube into the tire all the way round, tucking it up inside the casing.
4. Work the bead back on with your thumbs, starting at the valve and working both ways round to finish opposite it. Push the bead into the rim’s centre channel as you go — that’s where the slack is, and it’s why the last section is always the hard one.
5. Avoid levers if you possibly can. If you must, Park Tool warns: “Use care when using tire levers to avoid pinching inner tube.” A lever on the final section is the classic way to put a brand-new hole in a brand-new tube and discover it at 60psi.

6. Check the bead before you inflate properly

Do not just pump it up. Push the valve up into the tire and pull it back down — that frees any tube trapped under the bead at the valve, which is where it always is.

Then put a little air in and look. Park Tool: “Inflate to low pressure and inspect bead again on both sides. Look for small molding line above bead. This line should run consistently above rim.” That moulding line is a machined-in straightness gauge, and reading it is a genuinely useful skill. It should be an even distance from the rim the whole way round. Where it dives under or bulges up, the tire isn’t seated.

Park Tool’s warning on that is emphatic: “This bead seat line is bulging upward from improper tire seating. Deflate immediately and reseat tire.” Immediately. An unseated tire at full pressure can blow off the rim, and it is loud, sudden and can happen at speed.

7. Inflate, and reinstall

Up to pressure — “Inflate to full pressure and check with pressure gauge”, though at the roadside you have a mini pump and a thumb, and the thumb is what you’ve got. Park Tool also notes something that catches people out with Presta valves: “It may be necessary to press downward above the valve in order to engage the pump head.” Support the valve with your other hand while you pump — an unsupported Presta stem levered sideways by a mini pump is how you tear the valve out of a tube you just fitted.

Wheel back in, brake done up, quick release properly closed. Check the wheel spins straight and the brake isn’t rubbing before you get back on. Then top it up properly at home with a floor pump — the Topeak JoeBlow’s listing publishes a 160 PSI ceiling and a 3in analog gauge, which is the real difference: a gauge you can read, and pressure you didn’t have to earn. Getting the pressure right afterwards matters more than most people think — our tire pressure guidecovers what it’s costing you.

If you’re running tubeless

Mostly, you don’t do any of this — the sealant handles it while you keep riding, which is the entire point. When it doesn’t, the procedure above is exactly what you fall back to: take the valve out, fit a tube, and finish the ride with latex on your hands.

Park Tool’s published position is blunt — “in general, punctures in tubeless tires cannot be repaired”, with vulcanising patches viable only on UST and butyl-lined tubeless tires. So the tube in your pocket is not optional just because you converted. Tubeless vs tubes has the honest version of that trade-off.