Run-flat tyres are a special type of pneumatic tyres which are capable of supporting a car even after they suffer major punctures. The tyre is designed to allow the car to run at reduced speeds (under 80 km/h) as it helps in resisting the effects of deflation after a puncture. The distance these tyres can cover while completely deflated is limited and varies from 20-80 kilometers.
The reason these tyres are given such capabilities is mainly to help the driver reach a safe place or a repair shop after he suffers a flat. It's a kind of an emergency feature that makes sure that drivers don't get stranded due to a flat. It also increases convenience as you don't have to stop and change tyres. You can simply keep moving, albeit at a limited speed.
There are mainly two ways these tyres are able to achieve their run-flat nature:
1) Self Supporting System
In the Self Supporting System, the sidewall of the tyre is reinforced with steel layers which allow the tyre to take the weight of the car even after it has suffered a puncture. This allows the tyres to be functional even if the majority of the air pressure has been lost.
2) Support Ring System
The other one is the Support Ring run-flat tyre which has a ring made of hard rubber or another similar structure in the middle of the tyre. This ring helps support the vehicle's weight in the event of a major puncture that results in massive air loss.
Most of the tyre brands which offer run-flat tyres use self-supporting tech in them.
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Important Note: Since these run-flat tyres continue to perform even after they're flat, it is important that these tyres should always be used in tandem with a Tyre Pressure Monitoring System or TPMS. The TPMS will make sure that the driver is alerted as soon as any tyre starts to lose air pressure. Without it, you might never know that you're driving on a punctured or underinflated tyre.
Identifying Run-flat Tyres through Tyre sequence
There is a simple way to differentiate a run-flat tyre from a normal tyre. Simply pay attention to the sidewall of the tyre and look for these specific markings.
- RFT: Run-Flat Tyre; tyres designed for vehicles without spare tyres.
- ZP: Zero-Pressure; Michelin's branding for their run-flat models.
- RSC (inside a circle): BMW Runflat System Component
Pros of run-flat tyres
1) Usability - Run-flat tyres can be used even after a big puncture and can run for around 20-80 kilometres with a speed of up to 80km/h. They don't need to be replaced or re-inflated after the puncture as the tyres have enough strength to tolerate the weight of the vehicle even when they lack proper air pressure.
2) Offers better composure after a puncture - Run-flat tyres offer much better composure in any tyre-related accident as compared to a regular tyre. It is a life-saving feature, especially at high speeds.
3) Increases boot space - There is no need to carry a spare wheel in the boot if your car runs on such tyres. They can help you reach any tyre repair shop easily even after you've suffered a puncture and then you can simply get your tyre repaired or replaced.
Cons of run-flat tyres
1) Poor ride quality - Because of the added strength in the sidewall or the centre of the tyre, they don't offer a great ride quality as they can't absorb shocks easily and aren't as flexible on bumps because of their added rigidity.
2) Poor handling - Once the tyre gets punctured, it does retain its composure but doesn't offer the same handling and performance as before.
3) Very expensive - Run-flat tyres cost around 25-30% more than a regular tyre which is a lot of money. Their price tag certainly does not justify their limited benefits.
4) Have more weight - Because of the added strength, the weight of a run-flat tyre is around 40% more than a normal tyre which adds to the total weight of your car. This increases rolling resistance which reduces your fuel economy.
5) Hard to repair - Run-flat tyres are hard to repair and some manufacturers don't even allow repairing a run-flat tyre if it gets punctured. This is because it's difficult to spot secondary structural damages that may have been caused by running the tyres on the run-flat system. The replacement cost of a run-flat tyre is much more expensive than that of a normal tyre.
6) Tyre noise - Thanks to the added weight, strength and rigidity, tyre noise gets a substantial boost as well. Certainly not good news for the ones who prefer a quiet ride.
Run-flat tyres are a great option for heavy and armoured vehicles as they ensure that these can be driven even after a big puncture. However, for the average car owner out there, the negatives certainly outweigh the positives. Yes, they do allow us to drive without changing our tyres but their huge replacement cost and poor ride quality is certainly underwhelming.
Image Credits: Bridgestone
