Tire plug vs patch: which repair do you need?

What is a plug, a patch and a plug-patch?

A plug is a rubber strip or stem that fills the hole. A patch is a rubber sheet glued to the inside of the tire, and a plug-patch is one piece that does both.

A plug is the sticky cord you see in roadside kits. It is pushed into the hole from the outside with a tool, and the end is trimmed. A patch goes on the inner liner, the airtight layer on the inside of the tire. The one-piece plug-patch has a stem that fills the hole and a flat head that seals the liner.

Which repair does the tire industry call proper?

The U.S. Tire Manufacturers Association (USTMA) says a plug or rubber stem must fill the hole and a patch must seal the inner liner. The tire must be removed from the wheel for a full inspection first.

USTMA states it plainly: "A plug alone is an unacceptable repair." It also says never to do an outside-in repair or an on-the-wheel repair. Those are the two shortcuts most roadside kits rely on.

• Fill the hole, so water and dirt can't get into the belts.
• Seal the liner, so air can't leak around the plug.
• Inspect the inside, so hidden damage isn't missed.

Which holes can be repaired?

Only holes in the tread, ¼ inch (6 mm) across or smaller. Nothing that reaches the shoulder or the sidewall, and no repair that overlaps an old one.

• Tread area: the flat band that touches the road.
• Size: ¼ inch (6 mm) across, at most.
• Shoulder or belt edge: not repairable. If nobody can tell, USTMA says the tire comes out of service.
• Old repairs: a new repair can't overlap one. A tire with an old improper repair must be scrapped.
• Some tires, such as run-flats: the maker may set its own limits.

Measure the hole, not the object. A screw head can look small while the shaft left a wide channel. A torn or jagged hole is harder to judge, and the inspection decides it.

For the sidewall, see can a sidewall be repaired. For nails and screws, see nail in your tire.

Why does the tire have to come off the wheel?

Because the damage you can see from outside is only part of the story. A tire that ran low on air can be hurt on the inside, and only an inside look shows it.

When a tire loses air and keeps rolling, the sidewalls flex much more than they should. That can mark or weaken the inner liner. From the outside, the tire may look normal. Inside, a technician can look for rubber dust, creases, cuts and loose cords before deciding.

That is why a repair done with the tire still on the wheel skips the most important step. It may hold air, but nobody has checked whether the tire is safe to keep.

What happens in a proper repair, step by step?

The tire comes off the wheel, gets inspected inside, and the hole is filled and sealed from the inside. Then the tire goes back on and is checked for leaks.

1. Find and mark the hole, then let the air out.
2. Take the tire off the wheel so the inside can be seen.
3. Inspect the inside for creases, cuts and rubber dust from running low.
4. Check the location and size. Tread only, ¼ inch (6 mm) at most.
5. Prepare the hole and the liner so the repair can bond.
6. Fill the hole and seal the liner, with a plug and patch or a one-piece unit.
7. Refit the tire, inflate it and check for leaks.

If step 3 or step 4 fails, the answer is a new tire, not a bigger repair. That is the point of looking first.

When is a tire not worth repairing?

When the damage is outside the repair rules, or the tire is near the end of its life anyway. A careful shop tells you before doing the work.

• The hole is in the shoulder or the sidewall.
• The hole is wider than ¼ inch (6 mm).
• The tire was driven flat and is damaged inside.
• A new repair would overlap an old one.
• The tread is worn down to the wear bars.
• The rubber is cracked from age.

How long does a plug last?

There is no safe number to give, because the industry does not accept a plug alone as a repair. If your tire has an outside plug, have it inspected off the wheel soon.

Some drivers report plugs that hold air for a long time. Holding air is not the same as being safe. An outside plug leaves the inside unchecked and the liner unsealed, and moisture can travel along the hole into the steel belts.

• Plugged on the road? Treat it as a way to reach a proper inspection.
• Bought a used car with a plugged tire? Have it checked.
• Plug leaking or bubbling? Replace or properly repair the tire.

Can you plug your own tire?

Plug kits are sold everywhere, but USTMA says never to repair a tire from the outside or on the wheel. If you use one to get off the road, have the tire checked properly soon.

Plug kits also take strength and care. The reaming tool can push debris deeper, and a plug set at an angle can leak. Never use a kit on a hole near the edge or in the sidewall. If you are on a busy road, don't try at all: get to safety first, as our flat on the interstate guide explains.

Is a patch alone enough?

No, not by the USTMA rule. The patch seals the liner, but the hole itself must also be filled with a plug or rubber stem.

An empty hole through the tread lets water reach the steel belts from the outside. Over time that can rust them and weaken the tire. The plug part closes that path, and the patch part keeps the air in.

Can a run-flat tire be repaired?

It depends on the tire maker. USTMA notes that some makers set limits or rules for repairing run-flat tires, so check the maker's policy first.

Run-flats are built to keep rolling with no air for a short distance. That same driving can damage them inside. Your owner's manual or the tire maker's website usually says whether a repair is allowed.

What does Tire Amigo do with a flat?

A tire tech we work with checks the tire where the car is parked and tells you, before any work, whether it can be repaired. If a full repair can't be done at the car, you hear that first, with your options.

• Your good spare can go on, so you can drive to a proper repair.
• A new tire in your size can be fitted at the car.
• You get the all-in price by text before anyone drives out.

More on flat tire repair at your car and mobile tire replacement.

When to contact us: Nail or screw in the tread and the tire still holding air? Send us your details with the tire size and where the car is.