So you've had a flat tyre, what now? The most immediate need when you have a flat tyre is to get back on the road. You will usually have to address this by removing the punctured tyre and fitting your spare, safely out of the way of any traffic. However, it is critically important to organise for the punctured tyre to be repaired as soon as possible. This is especially the case if your vehicle's spare tyre is a space saver (or speed limited).
Before you repair your tyres you need to be certain they are worth repairing. Though often the reverse is true and tyres are removed prematurely from a lack of understanding of how to read tread depth indicators. A flat tyre never happens when it’s convenient. You can avoid a completely flat tyre in many cases by acknowledging the symptoms.
Symptoms of a tyre leak
- As you’d expect, a flat tyre is the most common symptom of a tyre leak.
- The steering pulls to one side.
- The suspension may feel softer than usual.
- The bottom of one tire is bulged out more so than the others.
How is the tyre repair performed?
- A technician locates the hole with soapy water.
- The hole is reamed to clean it, and the inner liner is prepped with a rasp.
- A liberal dose of rubber cement is applied to the area where the patch will rest, then a plug-patch is inserted.
- The plug fills the void in the tyre and provides some sealing.
- The patch is then pressed against the inner liner, completing the seal.
- The tyre is re-installed on the rim and rebalanced.
Tread Wear Indicators
All road going tyres are legally required to have Tread Wear Indicators, (TWI). For vehicles with a Gross Vehicle Mass, (GVM), of 4.5 tonnes or less, a tyre must have a tread pattern around its circumference that is at least 1.5mm deep across the entyre surface which comes in contact with the road. These are small raised platforms of rubber moulded into the main tread grooves. TWI’s are located in the tyre by the following indicators located in the shoulder of the tyre:
- The letters ‘TWI’
- A small triangular arrow head shape (see below)
- Sometimes by a company brand logo , (Goodyear ‘Wingfoot’ the ‘Michelin Man’, etc.)
So once you have located the TWI’s on your tyres it is time to determine if your tyres are worth repairing. While tyres are designed to provide thousands of kilometers of excellent service, there are typical conditions that might mean your tyres need to be removed:
- The tyre’s tread has worn down to the Tread Wear Indicator, (TWI)
- A road hazard or debris has damaged the tyre
- The tyre is fatigued from being run underinflated or overloaded
Tyre Repair Precautions
- Not all tyres can be repaired. The limits on whether they can be repaired should be based on recommendations or the repair policy of the tyre manufacturer and/or tyre servicers.
- Repair units should never overlap. The number of repairs need to be limited by the tyre manufacturer’s recommendations and repair policy or as determined by the inspection process.
- Some run-flat technology tyres cannot be repaired . Consult tyre manufacturer for their repair policy.
- Industry recommended repair methods include: (1) Two-piece stem and patch repair components, and (2) one-piece patch/stem combination repair units.
- Never perform a tyre repair without removing the tyre from the rim/wheel so as to be able to conduct an internal inspection.
- Never repair tyres with a tread puncture 6mm or over.
- Tyre changing can be dangerous and should be done by trained personnel using proper tools and procedures.
The basic principles for tyre repair
- To remove the tyre from the wheel for inspection and repair
- To prepare the injured area
- Fill the damage cavity with a suitable, vulcanizing material or rubber stem to completely fill the injury and keep moisture out
- To seal the inner liner with a patch repair unit to prevent air los
- To re-inspect the finished repair
In case of a flat tyre, you must gradually slow down and come to a standstill on one side of the road. If you continue to drive, you can end up damaging your tyre and wheel or if travelling at speed be responsible for an accident.
Common Causes of Tyre Punctures
- Slow or rapid deflation of a tyre
- Sharp object penetrating tyre while driving
- Failure of a tyre's valve stern
- Breakage of the link between a tyre and rim owing to a collision with an external object.
- Excessively worn out tread causing explosive tyre failure or debris from the road tearing through the tyre
When to Repair and when to Replace a Tyre?
There is an Australian Standard that regulates the repair materials used and the total number of repairs to be carried out on a tyre, based on the tyre size and location of the puncture.
A tyre must be thoroughly inspected before repair. Repair must not go ahead if any of the conditions below are present:
- Tread depth is below the legal limit of 1.6mm
- Compromised structural integrity
- Tread punctures are larger than 6mm
- Worn out, deteriorated rubber
- Any sign of previous faulty repairs
In case you are uncertain about whether your car tyre should be repaired seek expert advice.
Manufacturers policy on repaired tyres
Some manufacturers allow tyres to retain their speed rating if the specified multi-step repair procedure is followed exactly. But because manufacturers have no control over the state of the puncture or the quality of the repair, they judge the high speed capability of the tyre to be compromised.
The Rules of Repair
The 3 primary considerations when repairing a puncture are:
- Evaluate the damage the object has caused
- Reestablish an airtight seal of the tyre's inner liner
- Completely fill the path the object took through the tyre.
Typically, a mushroom-shaped patch and plug combination repair is the best method of repairing a punctured radial tyre.
Take the tyre off and repair both sides
Repairs require the removal of the tyre. Without inspecting the inside of the tyre for hidden damage the repair can be incomplete. Allowing the tyre to be inspected internally also applies to the rule that the puncture has to be sealed from both sides, as proper repair has to treat both the inside and the outside of the tyre. The one exception to this rule is an external plug can be used as a temporary measure when the puncture occurs in remote locations.
Fill puncture path
Repair has to fill the path the object took through the tyre. Otherwise moisture can seep in from the opening of the puncture to reach the steel belts and/or casing cords. This exposure can cause rusting or deterioration and further compromise the structural integrity of the tyre.
Treat inner tube
To repair the inner-liner it must be cleaned, buffed, cemented, patched and coated to restore its ability to retain air. This can only be done from inside the tyre and another reason why plug-only repair is unwise.
Tips to remember
- A sidewall puncture in your tyre is unrepairable. The sidewall and tyre shoulder area flex a great deal so tyre patches would quickly come loose. Instead, your tyre will need to be replaced.
- Impacting a curb or hitting large potholes can crack your rim where the tyre bead seals. If you’ve hit something and your tyre is now flat, you may require additional repairs above and beyond a tyre repair.
- Tyre patches alone and tyre plugs alone are not acceptable tyre repairs. The only approved tyre repair is the combination plug-patch style.
If you drive on a very low or flat tyre, you’re likely to damage the inner lining and sidewall. The result is a tyre replacement where a repair would have been sufficient previously, meaning an increased cost. In the workshop, the tyre is removed from the wheel and repaired in line with the Australian Tyre Repair Standard. Run flat tyres (otherwise known as mobility) tyres are becoming more popular as an original equipment manufacturer’s fitment to new cars, particularly for BMWs. This technology allows you to get home and to the store safely at a reduced speed and range without the need to change the tyre. The speed restriction for run flat tyres is generally 80 km/h with a distance restriction to travel less than 80km on these tyres. For advice on run flat and self sealing tyres, ask in-store. Run flat tyre repairs would be conducted in accordance with the Australian Tyre standard and in line with product specific recommendations from the world class manufacturers. Good luck!