What Are Run Flat Tyres

There’s often a lot of technical jargon surrounding tyres that can leave some drivers feeling confused. While you might have heard of run flat tires, you might not know exactly what they are or what their purpose is. So - what are run flat tyres? In short - they’re essentially tyres that allow you to come to a safe and controlled stop in situations where you have a punctured or flat tyre. That’s the short-hand version - but those in need of more detail, we’ve put together this guide on everything you need to know about run flat tyres, how they work - and whether you might need them yourself.

Do I Have Run Flat Tyres?

The majority of modern cars now come with run flat tyres as standard. If you don’t already have a spare tyre secreted in the cavity of the boot of your car or a foam filler tyre repair kit, then chances are your car is already fitted with run flat tyres (although it is worth checking this to be sure in case you’re not certain).

I Have Run Flat Tyres - Can I Exchange Them For Non-Run-Flats?

While this might seem like a less expensive option, it’s generally not a good idea to swap existing run flats out for non-run flats. Run flat tyres often come as ‘Original Equipment’, which means they are the tyres the car was originally fitted with when it left the factory.

There are a number of reasons drivers may opt to do this: some people find that conventional tyres offer a smoother ride - while others find conventional tyres cheaper and more available. However: since cars with run flats have no need for a spare tyre cavity, in the event of a puncture you would be left without a spare tyre as a replacement, which could potentially leave you stranded.

For this reason, if you bought your car second hand only to find there was no spare tyre in the boot, it’s imperative that you check to see whether the tyres on the car itself are actually run flats.

Because any changes to or from run flats count as a material change to the vehicle’s configuration, you should always notify your insurer if you decide to change your tyres. It’s alway advisable to check your vehicle’s warranty as well - as any changes could also affect your car insurance policy.

How Are Run Flat Tyres Constructed?

The sidewalls of run flat tyres are specially reinforced, so that even if your tyres are punctured, you can continue to drive with them at a limited speed and for a short amount of time (typically a maximum speed of 50 mph for a maximum of 50 miles). This is so that you can reach your nearest mechanic, if they are within this distance (if they are not, you may need to call for roadside assistance).

How Do They Work?

The reinforced wall inside run flat tyres is designed to keep your car going for a limited time even with a puncture. Run flat tyres can be easily identified using the symbols on the sidewall of your tyre.

There are two main types of run flat tyre:

SSR (Self-Supporting Run Flat) Technology

SSR (self-supporting run flat) technology is based on a self-supporting reinforced sidewall. In the event of a puncture, the reinforced sidewall prevents the tyre from being crushed between the ground and the rim, while preventing the tyre from slipping off the rim. 

Internal-Support Ring

Internal support ring technology support ring technology operates so that when a tyre is deflated, it has a lightweight metal ring to rest on. This supports the vehicle and helps to maintain the shape of the tyre while keeping it in contact with the road.

This structure, which is intended to help improve safety and driver experience, is available from a wide variety of tyre manufacturers. There is no standard code indicating run flat capabilities, however many tyre manufacturers will have their own style of run flat codes and symbols to indicate whether or not a tyre has run flat capability. These may include various acronyms, depending on the type of technology used:

• ROF - run on flat
• EMT - extended mobility technology
• RSC - run flat system component
• ZP - zero pressure
• RSC - run flat system component

Tyre Pressure Monitoring Systems (TPMS)

An important consideration is that run flats must be used in conjunction with a Tyre Pressure Monitoring System (TPMS), which provides an automatic alert to let you know you have a puncture. This system senses when a puncture is in a run flat tyre - so for this to be accurate, you would need run flat tyres on all the wheels on your vehicle.

As a general rule, it is recommended to replace your run flat tyre as soon as you see a puncture or if your TPMS system has notified you of a drop in tyre pressure.

While run flat tyres can be retrofitted to cars, they’re generally not recommended for cars without TPMS, since your car will give little or no indication that the tyre pressure has dropped.

Another key thing to note is that if you do have a puncture, it’s vital not to ignore the 50 mile limit and to get the tyre changed as soon as possible. If you don’t, you risk damaging the structure of the wheel itself, which can be far more expensive than changing a tyre.

What Are The Advantages Of Run Flat Tyres?

There are several main advantages to having run flat tyres:

1. No spare wheel in the boot means additional space.
2. Less overall weight (from carrying a spare tyre) leads to improved mileage and efficiency.
3. No need to change the wheel at the side of the road (which can be potentially dangerous).
4. The strengthened sidewall is designed to help keep your car under control incase of punctures.
5. Due to their reinforced sidewalls, run flat tyres are also reputed to be less prone to blow-outs, where air is rapidly lost from the tyre (these can be potentially dangerous).

Disadvantages of Run Flat Tyres

In most cases, run flat tyres perform their function well in cases of punctures - but depending on the situation, you could run into difficulties: if you have a puncture on a sunday evening for example, you may need to wait until Monday morning to find an open garage where it can be replaced or fixed.

It’s also possible that during this process, your journey length may exceed the 50-mile tyre limit, especially if you then have to drive to your destination before making an additional trip out to the garage the following day.

Are Run Flat Tyres Expensive?

Alongside flat batteries, flat tyres are one of the most common causes of roadside breakdown callouts across the UK - so for peace of mind and safety, they can be well worth the investment.

Run flat tyres are generally more expensive - by about half the price - but for this you get additional safety in case of punctures, which can make them worth the additional cost. In general, most fitters agree that run flats should be replaced rather than repaired - however this can create additional cost in comparison to fixing or changing standard tyres.

How Do I Repair Run Flat Tyres?

Run flat tyres are generally quite hard wearing - although wear and tear and even damage is sometimes hard to avoid.

While some manufacturers suggest repairs may be possible under certain conditions (or as long as the work adheres to British Standard BS AU 159) - in general repairing a punctured tyre is not advisable, as once the reinforced sidewall of the tyre has been compromised, the durability, safety and strength of the tyre will be significantly lessened (if in doubt, speak with your tyre’s manufacturer for more information.

A key reason for this is that if the damaged or deflated tyre has already been driven on, there is no way a mechanic will be able to determine how long the tyre has been used for.

Since this information is important for assessing the state of the tyres and how best to fix them, many fitters will refuse to repair your run flat and may even consider a replacement. To find out more, speak with your local tyres Manchester or tyres Stockport specialist who can advise on fitting, maintenance and more.