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What is a British Standard Tyre Puncture Repair?

BSAU159 tyre repair step 11

There are various methods of repairing a punctured tyre, with numerous accompanying products to enable those repairs.

By far the three most common tyre puncture repair methods are;

  1. An external repair using tyre string
  2. An internal repair using a repair patch
  3. An internal repair using a combination repair patch and plug.

However, only a tyre repair using a combination tyre repair patch and plug (also known as a combi repair or mushroom repair) is regarded as Industry best practice, as this is the only one to seal the tyre throughout the entire damaged area.

As for the actual repair procedure, there is only one that is accepted by British Standard Institution. This tyre repair procedure is known as BS AU 159 and sets out the "specification for repairs to tyres for motor vehicles used on the public highway".

British Standard Tyre Repair Procedure

Step 1Remove the tyre from the wheel and have a tyre expert thoroughly inspect it both internally and externally. If any serious tyre damage is present, then the repair should not continue. BSAU159 tyre repair step 1
BSAU159 tyre repair step 2 Step 2Locate and mark the damage, taking out any foreign object still puncturing the tyre.
Step 3Prepare the puncture channel from the tyre inside of the tyre using a 6mm carbide mill cutter. BSAU159 tyre repair step 3
BSAU159 tyre repair step 4 Step 4Repeat the process, now from the outside of the tyre inwards, ensuring once finished the channel feels resistance free on the mill cutter.
Step 5Thoroughly clean an area 10mm to 20mm larger than the repair patch using a specific pre-buff cleaner and repair scraper. Make sure to remove all residues such mould releasing agents. BSAU159 tyre repair step 5
BSAU159 tyre repair step 6 Step 6Hold the patch in position and mark its outline on the inner liner.
Step 7Buff the inner liner to roughly 5mm beyond the marked area using an appropriate domed buffing rasp. Make sure that any raised ribs are left flat after buffing, leaving suede finish. BSAU159 tyre repair step 7
BSAU159 tyre repair step 8 Step 8Remove dust and extraneous material including wire particles, buffed rubber and fluffed cords.
Step 9Apply a specialist vulcanising accelerator solution to the puncture channel and buffed area. BSAU159 tyre repair step 9
BSAU159 tyre repair step 10 Step 10Insert the combination tyre repair patch and plug into the puncture channel.
Step 11Pull the combination tyre repair patch and plug outwards until the entire patch is flush with the inside of the tyre. BSAU159 tyre repair step 11
BSAU159 tyre repair step 12 Step 12Roll the reverse of the patch using a corrugated tyre stitcher. Roll from the centre of the patch outwards to remove any air bubbles, making sure the entire patch has solid contact with the buffed inner liner.
Step 13Seal the combination tyre repair patch and plug base and buffed area still exposed with an inner liner sealant. BSAU159 tyre repair step 13
BSAU159 tyre repair step 14 Step 14Cut the stem of the combination tyre repair patch and plug flush with the remaining tread of the tyre, after first mounting the tyre back onto the wheel and reinflating to the correct pressure.

 

British Standard Tyre Repair Rules

  • Tyre repairs for cars and vans are only permitted in the central 60% to 70% of the tyres nominal width (known as ‘Area T’), with this percentage differing as shown below, depending on the size of the tyre.
Repairable Percentage Area (‘Area T’) based on Nominal Section Width
Up to and including 155mm 60%
Between 155mm and 200mm 65%
Above 200mm 70%
Example - Tyre size 205/55R16;

 Nominal section width = 205mm

70% of this width = 144mm

This tyre is repairable within 72mm of either side of the tyre centre line.

  • The maximum diameter of the penetration hole left by the puncturing object is 6mm.
  • Repairs in Area T must not overlap one another.

NOTE: All the information on this page is relevant to what is considered a minor repair to a radial construction tyre fitted to a car and van. This information is not relevant to commercial vehicles, heavy plant or industrial vehicles. Major repairs such a repairs to sidewall damage are also governed by the same British standard but will need to be sent away to a specialist major repairer.

 

The RIGHT and WRONG way to repair a punctured tyre.

tyre-puncture-patch-repair

The right way to repair a tyre puncture

Waking up to find your car has a flat tyre is never good, especially if you have got the commute to work to contend with or a family road trip planned.

While almost any small object left on the road can cause a tyre puncture, sharp objects such as screws, nails and glass shards are the most common causes.

“Before agreeing to have any puncture repair carried out, make sure the tyre technician has removed the tyre from the wheel for a thorough inspection and that he or she intends to repair the tyre by the British Standard.”

Even though the damage may appear small, it is important to have the tyre inspected by an expert to ascertain the full extent of the damage, including whether there is any secondary damage caused by driving on the tyre at low pressure.

Assuming the tyre inspection does not find any tyre damage meaning the tyre should be replaced instead of repaired, two crucial aspects now need addressing in any subsequent tyre repair;

  1. Reestablishing the integrity of the airtight inner liner within the tyre
  2. Ensuring the path the object took through the tyre is filled

Of all the numerous tyre puncture repair options available, there are three that are used in by far and away, the vast majority of cases. Of these three, however, only one is considered industry best practice and a British Standard Repair.

That repair is the tyre repair using a combination tyre repair patch and plug (also known as a combi repair or mushroom repair).

Below shows an example of a proper combination tyre repair patch and plug repair, along with the two other common, incorrectly performed tyre repairs that are not British Standard.

CORRECT TYRE REPAIR
This type of a puncture repair is a combination tyre repair patch and plug (also known as a combi repair or mushroom repair). This type of repair achieves both the key points of consideration when correctly repair a tyre puncture.

types-of-tye-puncture-repairs

INCORRECT TYRE REPAIR
This type of puncture repair is known as a string repair and does not reestablish the airtight inner liner of the tyre. This type of puncture repair is known as a patch repair and does not fill the path the object took through the tyre.

 

Tyre repairs made externally, without removing the tyre from the wheel are never acceptable on modern car tyres. Without a proper inspection of the inside of the tyre, there could be any number of types of internal tyre damage that go unseen, therefore returning a tyre to the road that is unsafe.

Why a string or patch puncture repair is the wrong way

tyre-string-repairstring type of puncture repair is designed to be carried out from the outside of the tyre, meaning the tyre can not have a complete internal damage inspection.
The second problem is that this type of repair relies on the stickiness of the string to hold it in place in the path created by the puncturing object. However, the pressure of the air within the tyre, that will usually be upwards for 32 pounds per square inch will constantly be trying to push the string back out. Who will win, stickiness or air pressure?Finally, unless the string when inserted some the outside inwards, somehow manages to fill the entire puncture cavity created in the tyre’s inner liner, there will not be a truly airtight seal, and air will seep out around the string over time.
A puncture repair patch is installed from the inside, therefore allowing a thorough inspection of the tyre’s interior. It also fully reestablishes the tyres air tight properties by sealing over any part of the inner liner that is damaged. tyre-puncture-patch-repairHowever, a patch type of puncture repair does not fill the entire puncture cavity, so allowing moisture in and causing the now exposed steel tyre cords to corrode and rust. Once it has begun, this rusting can spread from the original puncture cavity along the tyre cords to the sidewall where the increased flexing in the sidewall can cause the now brittle cord to snap, producing a weak spot.This weakened spot in the tyre’s sidewall can then develop into a bulge due to the air pressure inside, which in the best case scenario will cause an MOT failure, or in the worse case scenario could cause a tyre blow out.

 

So, if your local garage offers to repair your punctured tyre in “just a few minutes”, for as little as £10; be wary. They almost certainly are not repairing your tyre to the British Standard. The British standard repair is a complex multi step procedure that will take upwards of 20 minutes when done properly.