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Tyre repairs and sealants

You might not need to buy a new tyre

Some tyre punctures can be repaired

If you get a puncture you might be able to get it repaired, for a fraction of the cost of a new tyre,  if:

  • the puncture’s in the main tread area, and
  • you stopped quickly without overheating the deflated tyre

A bodged repair could be very dangerous so a British standard (BS AU159) sets out clear rules for the type of damage that can and can’t be repaired and how repairs should be carried out.

Importantly the tyre has to be removed from the wheel to check for internal damage which could later cause sudden failure if not spotted.

This means that externally applied plugs and liquid sealants injected through the tyre valve can’t be thought of as permanent repairs.

Tyre repairs and sealants

Tyre sealants

It’s common for new cars to come with a tyre sealant and tyre-inflator pack instead of a spare wheel. The sealant and compressed air are injected through the tyre valve but the result achieved will depend on:

  • the cause of the puncture
  • the position of the puncture, and
  • how far and fast you’ve driven on the flat tyre

There are two basic types of sealant; pre-puncture sealants, put into the tyre in case of a puncture, and post-puncture sealants, put in following a puncture.

 Pre-puncture sealants

Injected through the tyre valve, the aim is to prevent air loss if a puncture does occur so you can drive on without interruption.

  • If the sealant works then the seal will be pretty much instantaneous which raises the concern that you’ll have no idea whether there's been a puncture or not.
  • A large screw or nail sealed’ into the tread could cause more damage over time, possibly leading to a blowout.
  • You should check your tyres every time you use the vehicle.  If the sealant’s been activated you should see signs of the sealant (usually white latex based) on the outside of the tyre.
Post-puncture sealants

With these, the hope is that you’ve spotted a puncture and stopped before the tyre has overheated or become shredded to pieces on the wheel rim.

  • The sealant is injected through the tyre valve and the compressor or cylinder of compressed gas is used to (hopefully) re-inflate the tyre.
  • Handy if you regularly drive alone, but won’t work for all punctures.
Permanent or temporary?

Whatever type of sealant you use, it can’t be considered a permanent repair because the tyre’s not been taken off the wheel to check for internal damage.

As well as laying down the size and location of damage that can be repaired, the British standard specifies the materials and methods that must be used to make a permanent repair, and includes the statement: "use of liquid tyre sealants does not meet these criteria and hence cannot be considered suitable as a permanent repair."

17 January 2017

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