How to Fix a Tubeless Flat

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The rule that decides a tubeless roadside repair is this: do not break the bead until you have to. Every fix below is ordered by how much of the system it disturbs, and once the tire comes off the rim you have lost the sealant, the seal and the fifteen minutes it takes to get them back. Work up the ladder, not down it.

The other half of the discipline is knowing what each step can actually do. Sealant handles small holes. Plugs handle bigger ones. A boot handles a cut. A tube handles everything else and is why you still carry one.

Level 1 — Let the sealant work (and help it)

Most tubeless punctures are sealing before you notice them. If you feel pressure dropping and see a spray, the useful thing is to keep the wheel turning and rotate the hole to the bottom: sealant pools at the lowest point, so putting the puncture there and letting the wheel spin gets latex to the hole. Pressing a thumb over the hole for a few seconds while the tire is still at pressure often does the rest.

Then top up the pressure — a sealed hole at 15 psi will unseal at 45 — and ride gently for a minute before trusting it. If the sealant is old and has dried out, none of this works, which is the strongest practical argument for the top-up schedule in our tubeless setup guide.

Level 2 — Plug it

A plug (“bacon strip”, rope plug or DART) is inserted from the outside, with the tire still on the rim, and it fills the hole physically so the sealant can finish the job. This is the repair that keeps most tubeless riders from ever fitting a tube.

Stan’s publishes the useful limits for its own system. The DART is designed for punctures larger than 5 mm, and its treated fabric reacts chemically with latex-based sealant to form an airtight seal — with the important corollary that if the sealant in your tire has dried up, the DART cannot bond. Rope-style plugs work mechanically instead and do not care about the sealant chemistry, which is why plenty of riders carry both.

The technique, whichever plug you carry:

1. Find the hole while it is still hissing. Once it stops, you will not find it.
2. Leave the wheel on the bike if you can — you are working from the outside.
3. Push the tool in firmly and at an angle following the direction the puncture went in, not straight at the casing.
4. Withdraw the tool smoothly, leaving the plug in place. Do not twist a rope plug back out with the tool.
5. Reinflate, spin the wheel to distribute sealant over the plug, and check it holds pressure for a minute before riding.
6. Trim the excess flush only once it has held. Some riders leave it proud — it wears down on its own.

Level 3 — Boot it

A cut — as opposed to a puncture — is a hole with length, usually from a flint or a rock strike on the sidewall. No plug bridges a cut reliably, because there is no shoulder of casing for it to grip. What works is a boot: a stiff patch placed on the inside of the casing to span the damage and stop the tube or the sealant extruding through it.

Booting means breaking the bead, so you have already lost the sealant seal. Accept that, and finish the job properly: boot the cut, then fit a tube on top of the boot. Riding a booted tubeless tire on sealant alone is optimistic; a cut long enough to need a boot is usually a tire to replace when you get home.

Level 4 — Fit a tube

The universal fallback, and the reason every tubeless rider still carries one. Park Tool’s published position on tubeless repair is unsentimental — in general, punctures in tubeless tires cannot be repaired in the way an inner tube can be patched — so the tube in your pocket is not made redundant by the sealant in your tire.

Two tubeless-specific details that catch people out:

• The valve has to come out first. A tubeless valve is fixed through the rim with a lockring; it must be removed before a tube can go in. That lockring is often finger-tight-plus, and cold hands do not help.
• Everything will be covered in sealant. It goes everywhere. Get the tire bead clear of sealant where you can, because latex on the rim bed makes fitting a tube slippery work, and check the inside of the casing for whatever caused the puncture before the tube goes in.

The rest of the procedure is identical to a standard flat — two levers, check the casing, seat the bead evenly — and that is covered step by step in how to fix a flat.

CO2 and tubeless: the published warning

CO2 is the fastest way to re-inflate at the roadside, and Stan’s publishes a caveat that very few riders have read: CO2 is best used in an emergency, and Stan’s recommends letting the CO2 out after the ride and replacing it with regular air — because prolonged CO2 exposure can cause the sealant to separate and can degrade the liquid latex the sealant depends on.

So: use the cartridge to get home, then bleed the tire and re-inflate with a floor pump the same evening. That two-minute habit is the difference between sealant that works next month and sealant that has turned to lumps.

What actually prevents roadside tubeless repairs

Almost all of it is maintenance, not luck. Sealant dries out — a tire that has not been topped up in six months is running on latex-colored stains, and both the automatic sealing and the DART’s chemical bond depend on wet sealant being present. Pressure matters too: our gravel tire pressure guide works through why running too low invites pinch cuts and burps, and too high defeats the point of tubeless entirely.

And if you are still weighing whether tubeless is worth this at all, that is a fair question with an honest answer in tubeless versus tubes.

What we could not check

We have not plugged a tire on a rig, timed a seal, or compared plug brands under controlled conditions. The limits quoted here — the DART’s 5 mm threshold, its dependence on wet latex sealant, and the CO2 guidance — are Stan’s own published statements, read on 18 August 2026, and the repair ladder is standard workshop practice presented in the order that disturbs the system least.