What are ‘Run-flat’ tyres, and how do they work? What are the advantages and disadvantages of using them?
What are ‘Run-flat’ tyres, and how do they work? What are the advantages and disadvantages of using them?

We all know that the tyres are one of the most important bits of a car; those few square centimetres of rubber are what keep us connected to the ground while we drive.  But whilst there are many options as to what type of tyre you can buy, with all sorts of different noise, speed, and grip levels, there is another choice to be made, run-flat or regular?  But what are run-flat tyres exactly?  How do they work?  What are the upsides and downsides to using them?

What are run-flat tyres and how do they work?

Run-flat tyres are tyres designed to resist the effect of deflation when punctured.  There are three types of run-flat tyre:

  1. Self-supporting run-flat tyre: These tyres are much like regular tubeless tyres, but they have thicker, reinforced sidewalls for extra strength.  This enables them to retain their shape and rigidity when tyre pressure drops to a point that would usually result in a flat tyre.  This is the most common type of run-flat tyre, commonly found on premium vehicles such as BMW and Mercedes-Benz, often in place of having a spare tyre.  In the case of a puncture, one may continue driving on these at speeds of up to 80km/h for as far as 350km, tyre dependant.
  2. Self-sealing run-flat tyre: These tyres are similar to having tubed tyres.  They feature an inner lining that self-seals by means of pressure exerted on the inner lining in the event of a small puncture by a nail or screw.  These self-sealing tyres are able to prevent further air loss, or at least slow it down.
  3. Auxilliary-supported run-flat tyre: These tyres are similar to standard tubeless tyres, but the wheel features an additional support ring that is capable of supporting the vehicle’s weight in the event of tyre deflation.  Both special wheels and special tyres are required for this type of run-flat technology.
These cuttings of two tyres demonstrate how thick the sidewalls of self-supporting run-flat tyres (Bottom) are compared to regular tyres (Top)
These cuttings of two tyres demonstrate how thick the sidewalls of self-supporting run-flat tyres (Bottom) are compared to regular tyres (Top)

What are the benefits and drawbacks of run-flat tyres?

Run-flat tyres, as with all technology, carry with them a series of benefits and drawbacks:

The main benefit of run-flat tyres is the ability to continue driving with a puncture.  This means that you don’t have to pull over in a dangerous area to change a tyre late at night etc.  Additionally, many manufacturers who use run-flats don’t equip vehicles with spare tyres, saving space and weight in the boot of the car.  Stiffer sidewalls do also offer the benefit of being better performance tyres.  Because the tyre has less flex, it is less prone to understeering.

The drawbacks of run-flat tyres are more numerous than their benefits.  Firstly, run-flat tyres, due to the stiffer sidewalls, make for a more uncomfortable drive.  The tyre does not have the same compliance over poor surfaces and relays smaller bumps into the cabin far more than regular tyres.  Run-flat tyres are also heavier, and as such have a higher rolling resistance, which can reduce fuel efficiency.  Another drawback to run-flat tyres is that although for the most part they are safe, they are more rigid and are more prone to being damaged by objects such as cat-eyes and potholes.  This may cause severe blow-outs, in which case you’re not likely to have a spare tyre to use.  The tyres are also more expensive and as such cost more when the time comes to replace them, either due to wear and tear or the aforementioned blow-out.

Which tyre is best?

At the end of the day, it comes down to personal preference.  The benefits of run-flat tyres are fantastic, but the drawbacks are equally as concerning.  Should your vehicle not come with run-flats, and you’re in the process of buying new tyres, you would need to weigh up the pros and cons of each.  We at TCR are advocates of a more compliant ride and a spare tyre should anything go wrong, but as the saying goes, each to his own.

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