In short. A plug pushed in from the outside is a roadside fix, not a repair. The repair that the tyre makers' rulebooks accept takes the tyre off the wheel, inspects it inside, fills the hole with a rubber stem and seals the inner liner with a patch, usually as one mushroom-shaped piece. The US makers' association (USTMA) says it in capitals: a plug only or a patch only is "NOT ACCEPTABLE". In Britain the reference is BS AU 159G:2013, whose scope leaves out externally inserted plugs; in Australia, AS 1973-1993 leaves them out too. The repair has to be in the central part of the tread and the hole no wider than 6 mm (a quarter of an inch). What a repair does to the speed rating and whether a run-flat can be repaired at all depend on the tyre's maker, and the makers disagree.
Plug, patch and plug-patch: three different things
A plug (a string, wick or "cord") is a strip of sticky rubberised material pushed into the hole from outside, with the tyre still on the car. Nobody looks inside the tyre.
A patch is a rubber disc bonded to the inner liner, with the tyre off the wheel. It seals the air in, but it leaves the hole through the tread open.
A plug-patch (a "mushroom", or "combination unit") is both at once: a stem that fills the hole and a patch that seals the liner, fitted from the inside after the tyre has been demounted and inspected.
The reason the rulebooks insist on both halves is in the tyre's structure. Michelin UK says a patch alone is "not recommended because it will seal on the inside, but not between the tread and the inner rubber", which leaves a path for water to the partly metallic layers and a risk of the tyre bursting. Of a wick, it says the repair is "strongly disadvised" because nobody checks the inside after the tyre has run soft. Continental is shorter: "A plug is not a repair." Its page goes further than the others: "Due to safety reasons Continental would never recommend to repair a tire but exchange it."
The check inside matters because a tyre that keeps rolling while soft has its sidewall crushed. Michelin UK says that if the carcass has been damaged, "your tyre is too weak and cannot be repaired, even if the puncture was in the tread". A plug fitted at the roadside hides exactly that.
What each rulebook says
We read the documents where they are free, and the official scope where the full text is sold.
| United States | United Kingdom | Australia | Canada | |
|---|---|---|---|---|
| Reference | USTMA puncture repair procedures (wall chart, © 2025) | BS AU 159G:2013, published 30 November 2013, status "Current" | AS 1973-1993, published 15 November 1993, "Pending Revision" | No national repair standard found; Michelin Canada's page sets the same limits as the US chart |
| Accepted method | A plug to fill the injury and a patch to seal the liner | Permanent repair; the standard covers inspection, performance, materials and marking | In-service repairs covered | A "patch-plug combination" from the inside, tyre demounted (Michelin Canada) |
| Outside plug | "NEVER perform an outside-in tire repair or on-the-wheel repair" | Out of scope: "temporary seals, i.e. externally inserted plugs" | Out of scope: "externally applied plugs or liquid puncture sealants" | "Do not have your tire plugged. Ever." (Michelin Canada) |
| Largest hole | 1/4 inch (6 mm) | 6 mm, as Pirelli UK reports the standard | Not in the scope we could read | 1/4 inch on the main page, 6 mm in its FAQ |
| Where | Tread only; never the shoulder or belt edge | The "T area", the central part of the tread | Not in the scope we could read | Central tread; not the shoulder, sidewall or bead |
Three points stand out. First, no rulebook accepts an outside plug as a permanent repair: the US chart forbids it, and the British and Australian standards simply do not cover it. Second, the British and Australian texts are paid documents; the limits that reach the public come through manufacturers and fitters, as Pirelli UK's page does when it says BS AU 159 is "shared with the BTMA (British Tyre Manufacturers' Association)". Third, the USTMA chart itself says specific repair limits "should be based on recommendations or repair policy of the tire manufacturer", so the maker of your tyre has the last word. We could not find the Tire Industry Association's own policy online, so we do not quote it.
Where on the tread a repair is allowed
Every source agrees that the sidewall and shoulder are out (a bubble on the sidewall is a different problem, covered in tyre bulge on the sidewall). They describe the repairable band differently.
- Pirelli UK: "The T area is the area between 60% and 70% of the tyre's nominal width."
- Continental: "the central three-quarters of the tread"; a British fitting chain: "the central ¾ of the tyre".
- USTMA: the tread area, and never where the injury reaches "the shoulder/belt edge area OR where the injury extends at an angle into the shoulder area".
- Goodyear's bulletin for speed-rated tyres: "within the outside grooves".
To make those percentages usable, we converted them into millimetres on four common section widths. This is our arithmetic. The "band" is how far in from each side of the nominal width the non-repairable strip runs.
| Section width | T area at 60 % | T area at 70 % | Band each side (T area) | Three-quarters of the nominal width | Band each side (three-quarters) |
|---|---|---|---|---|---|
| 205 mm | 123 mm | 143.5 mm | 31 to 41 mm | 153.8 mm | 26 mm |
| 225 mm | 135 mm | 157.5 mm | 34 to 45 mm | 168.8 mm | 28 mm |
| 255 mm | 153 mm | 178.5 mm | 38 to 51 mm | 191.3 mm | 32 mm |
| 285 mm | 171 mm | 199.5 mm | 43 to 57 mm | 213.8 mm | 36 mm |
Two cautions. The section width is measured across the sidewalls, so the tread itself is narrower than the first number on your tyre; the tables give an idea of scale, not a template. And the two descriptions do not measure the same thing: Pirelli's percentages are of the nominal width, while Continental's three-quarters are of the tread, which is narrower; the last two columns apply three-quarters to the nominal width, so they show the widest reading of that rule, not Continental's own figure. Even so, Pirelli's band is the wider of the two (34 to 45 mm against 28 mm on a 225). When the sources differ, the fitter applies the stricter one or the tyre maker's own rule; the size reading on the sidewall is explained in how to read a tyre size.
How big a hole: 6 mm or a quarter of an inch
A quarter of an inch is 6.35 mm. The USTMA chart writes "1/4-inch (6mm)", Pirelli UK gives a "maximum diameter of 6mm", Continental's page says repair is not permitted "if the puncture is 6 mm or larger", and the British fitting chain says the puncture "needs to be less than 6mm". So a hole of 6.2 mm is inside the US figure taken literally and outside the British readings. A typical nail or screw is well under either limit; for a bolt or a cut, the strictest reading should win. The hole is measured by the fitter after cleaning it out, with the tyre off the wheel, which is one more reason a roadside plug cannot settle the question.
Size is not the only test. Michelin's US, Canadian and Australian pages add that the tyre must not have been driven flat. Michelin Canada says a tyre with "multiple punctures" cannot be safely repaired; the USTMA says repairs "cannot overlap" and that a tyre with "an existing, improper repair" must be scrapped. Goodyear's bulletin and Michelin's 2011 Canadian manual both refuse to repair a tyre worn below 2/32 of an inch (1.6 mm).
Is a plugged tyre safe?
As a way to reach a fitter, it is what plug kits are sold for, and Michelin Canada calls a plug kit "a temporary emergency measure". As a permanent fix, no maker we read accepts it. Michelin US says plug-type repairs on a tyre that stays on the wheel "are improper and can result in an accident". Michelin UK says a repair kit, whether a foam spray or a tool that fills the hole from outside, is a "last resort" to get you to the nearest garage.
None of the sources we read gives a speed or distance for driving on a string plug. Treat it as the shortest drive to a fitter, check the pressure before you set off and again on the way, and tell the fitter it has been plugged. If the tyre has run soft for any distance, or the plug sits near the shoulder, do not drive on it: change to the spare or have it checked before you take the road again. Michelin Canada says to have any plugged tyre "demounted and properly patch-repaired—or replaced" as soon as possible. The USTMA chart is stricter: "NEVER repair a tire that has an existing, improper repair; the tire must be scrapped", and by its own rule a plug alone is improper. So whether a plugged tyre can still get a proper repair is the fitter's call, made with the tyre off the wheel; do not count on it.
If you are changing to the spare at the roadside rather than plugging, the safety points are in how to change a wheel safely: the jack holds the car only while you swap the wheel; never put any part of your body under the car unless it is raised and resting on axle stands. What you carry instead of a spare, and what it can do, is in spare wheel, space saver or repair kit.
What a repair does to the speed rating
This is where the published rules disagree most. The speed rating is the letter after the load index (Goodyear's bulletin puts H at 130 mph, 210 km/h).
| Source and date | What it says about speed after a repair |
|---|---|
| Pirelli UK | Tyres repaired to BS AU 159 "offer the same performance as a healthy tyre, in terms of durability, load capacity and maximum speed tolerated" |
| Goodyear, bulletin 2003-06 (23 April 2003) | For H and above: one repair, 6 mm, in the tread within the outside grooves; a tyre repaired "in strict accordance" keeps its rating; an incorrect repair means it is "no longer being speed-rated by Goodyear"; a larger section repair invalidates the rating |
| Michelin, Canadian owner's manual (2011) | Speed ratings are not applicable if tyres are "improperly repaired" |
| Michelin UK (updated 8 September 2026) | A sidewall hole of 3 mm or less can be repaired only if the rating does not exceed T; "Beyond this index, tyre repair is strongly disadvised" |
| A British fitting chain | "Any tyres rated 'V' and above can only have one puncture repair in the lifetime of the tyre" |
| AS 1973-1993 (Australia), scope | Does not permit major repairs in passenger car tyres of speed category "'V', or higher" |
Read together: a correct plug-patch in the tread keeps the rating for Pirelli and, within one repair, for Goodyear; a poor repair loses it everywhere; and for a tyre rated V or higher, a British fitter may refuse a second repair. Michelin UK's sidewall exception, for tyres rated T or below, is the only place we read that allows a sidewall repair at all, and it is the opposite of what Michelin's own US page says ("sidewall damage ruins a tire immediately"). We cannot reconcile the two; ask your fitter which rule applies to your tyre. The Goodyear bulletin dates from 2003; it is the latest Goodyear text on the point we could read.
Run-flat tyres
| Source | Repair a punctured run-flat? |
|---|---|
| Michelin UK (ZP and EMT tyres) | "Runflat tyres can be repaired once" |
| Michelin US | "Sidewall damage, run-flat damage, and any tire that was driven flat require replacement" |
| Pirelli UK | "Manufacturers advise against repairing RUN FLAT tyres"; they "should not be repaired but replaced", though "it all depends on the individual case" |
| Continental | "Most manufacturers advise against patching run-flat tires" |
| A British fitting chain | A punctured run-flat "will need to be replaced" |
| AS 1973-1993 | Does not apply to "limited-run-flat" tyres |
| USTMA | Some makers set "repair limits or restrictions" for run-flats |
The likeliest reading of the two Michelin pages is that a run-flat punctured and stopped promptly may be repaired once, while one that has been driven in run-flat mode has "run-flat damage" and is replaced; that is our interpretation, not Michelin's wording. Pirelli's reason: the stiff sidewall can hide damage done while running flat. Pirelli says a punctured run-flat can generally cover up to 50 miles at a maximum of 50 mph; the figures on your tyre and in your car's handbook come first.
How many repairs?
Pirelli UK says that under BS AU 159 there is "no limit to the number of minor repairs that can be made to a tyre's T area, as long as they are not superimposed". The USTMA says repairs "cannot overlap". Goodyear allows one on tyres rated H and above; the British fitting chain one on V and above. Michelin Canada's FAQ excludes a tyre with multiple punctures. On a tyre rated H or V and above, several of these rules allow only one.
What the law says
Great Britain. No regulation we found prescribes how a tyre is repaired. Regulation 27 of the Road Vehicles (Construction and Use) Regulations 1986 judges the tyre, not the repair: a car must not be used if a tyre has a cut "in excess of 25 mm or 10% of the section width of the tyre, whichever is the greater" and deep enough to reach the ply or cord, has "any lump, bulge or tear" from a failure of its structure, has "any of the ply or cord exposed", or "is not maintained in such condition as to be fit for the use". We searched section 5 of the MOT inspection manual for a defect that mentions a repair, a plug or a sealant and found none; the tester checks size, condition, tread and fitting. BS AU 159G is a British Standard, not a law, but it is the reference fitters work to.
United States. We found no federal rule on the method; the USTMA chart is the industry procedure and tyre makers' policies sit on top of it. We could not open NHTSA's consumer tyre booklet (access refused), so we do not quote it.
Australia. AS 1973-1993 covers in-service repairs and leaves externally applied plugs out of its scope. States publish their own vehicle standards guidance; Victoria's guideline on tyre maintenance and repair refused our reader, so we do not quote it.
Canada. We found no national repair standard; Michelin Canada's page sets the same limits as the US chart: tread only, 6 mm, tyre off the wheel, never a plug alone.
Before you go to the fitter. If a sealant from a kit or a plug has been used, say so before the tyre comes off: the fitter has to deal with it, and on a car with direct pressure monitoring the sensor sits inside the wheel, on the valve (see MOT, TPMS and aftermarket wheels). After any repair, set the pressure to the car maker's figure on the door pillar or in the handbook (tyre pressure), and tighten the wheel to the car maker's torque. If the leak comes back and the tread is clean, the cause may be the valve or the wheel: slow puncture: causes and fixes goes through the five places air escapes.
Frequently asked questions
Is a plug or a patch better?
Neither on its own. The USTMA calls a plug only or a patch only "NOT ACCEPTABLE"; the accepted repair is a plug-patch fitted from inside, with the tyre off the wheel. A plug alone is a temporary fix to reach a fitter.
Is a plugged tyre safe to drive on?
For the drive to a fitter, with the pressure checked, it is what plug kits are for. As a permanent repair, no maker we read accepts it: Michelin US calls on-the-wheel plug repairs "improper", and Continental says "A plug is not a repair."
Can a plugged tyre be repaired properly later?
Sometimes, and only the fitter can say. Michelin Canada says a plugged tyre should be demounted and patch-repaired, or replaced, as soon as possible; that needs a hole in the central tread, no wider than 6 mm, and a tyre that was not driven soft. The USTMA chart says a tyre with an existing, improper repair must be scrapped, and it counts a plug alone as improper, so a fitter working to it may refuse.
What is BS AU 159?
The British Standard for repairs to road vehicle tyres, current edition BS AU 159G:2013. Its scope covers repairs, inspection, materials and marking, and excludes externally inserted plugs and liquid sealants. It is not a law, but it is the reference British fitters work to.
How close to the sidewall can a puncture be repaired?
Only within the central part of the tread: the central three-quarters of the tread for Continental, an area 60 to 70 per cent of the nominal width for Pirelli, never the shoulder for the USTMA. On a 225 tyre, Pirelli's T area leaves a strip of roughly 34 to 45 mm on each side of the nominal width where no repair is made.
Does a repair void the speed rating?
It depends on the maker. Pirelli says a BS AU 159 repair keeps the maximum speed; Goodyear's 2003 bulletin keeps the rating for one strict repair on H-rated tyres and above; a poor repair loses it for every maker. Some British fitters allow one repair in a V-rated tyre's life.
Can a run-flat tyre be repaired?
Michelin UK says its run-flats can be repaired once; Pirelli, Continental and a British fitting chain advise replacing them; Michelin US says run-flat damage requires replacement. Have a punctured run-flat checked by a fitter before relying on it again.
Is a plugged tyre an MOT failure?
We found no MOT defect for a repair or a plug. The tester checks the tyre's size, condition and tread; a cut, a bulge or exposed cord is a defect in its own right, repaired or not. A plug is still a temporary fix: have the tyre repaired properly or replaced before relying on it.
Where to go next
The tyre is the fitter's business; the wheel underneath it is ours. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards. Onyx Forged does not recommend a size or an offset, nor a tyre or a repair method: we explain, compare and send you to the documents of the car and tyre makers. See Onyx Forged.
Sources
- US makers' association: USTMA, puncture repair procedures for passenger and light truck tires (wall chart excerpt) and USTMA, tire repair basics.
- Standards: BSI Knowledge, BS AU 159G:2013 (the scope; the paid text is not read); NSAI, AS 1973-1993 and Australian Business Licence and Information Service, AS 1973-1993 (scope only).
- Tyre makers: Michelin UK, tyre repair; Michelin US, Michelin Canada and Michelin Australia, can my tire be repaired; Michelin, limited warranty and owner's manual, Canadian edition, 2011; Pirelli UK, tyre puncture repair; Continental, tire repair; Goodyear, product service bulletin 2003-06.
- Law and testing: legislation.gov.uk, Road Vehicles (Construction and Use) Regulations 1986, regulation 27; GOV.UK, MOT inspection manual, section 5.
- A fitter's rules: a British fitting chain, puncture repairs.
All pages were read on 16 October 2026.
The Onyx Forged design office.