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What's Inside a Bulletproof Run-flat Tire and how does it work?

Car tires are the backbone of any car. After all, these four round disks support the vehicle load, transmitting traction and braking forces to the road surface, absorbing road shocks, and steering the direction of travel which allows you to roll down the road smoothly. But before we dwell deep on it, let’s look at some fun facts that we are sure you don't know about car tires-


  • The first rubber car tire was invented in 1895 and was white in colour. In the 21st Century, carbon black, which came with benefits like increasing the durability and strength of the rubber became an adding agent that changed its colour to black. 


  • Tires of armoured vehicles can continue to be driven fast, safely and with stability for several kilometres even after the tires have been blown out.


  • Car manufacturer BMW outfits most of its cars with run-flat tires, despite being twice as expensive as the regular tires.


The above facts take us through a journey of car tires from the simple rubber ones to high-tech run-flat tires (RFT) that look exactly the same but as are have varied features. But, today let’s look at bulletproof RFTs. Though most of you may already know about it, but for those unfamiliar, these car disks or tires are uniquely designed to withstand the effect of deflation when punctured. Wrapped in silicone, these superheroes of the car if damaged can still be driven at a reduced speed of 90 km/hr for about 80 km, depending on the type of the tire.The RFT are considered to be an integral part of all armoured vehicles, a popular mode of transport for diplomats, ambassadors, political leaders, business people, and other celebrities. 


 So, let's look at some basic principles that drive the run-flat tires –



  • The car on which the RFT is fit must have functional wheel air pressure sensors. Without which, it is hard to analyse the problem.


  • If the pressure drops, inflate the damaged tire as soon as possible. This procedure will reduce the risk of permanent damage to the casing.


  • In case of a puncture, most manufacturers recommend against a repair of run-flats tires and advise a replacement. It is mainly because the design of these tires makes it difficult to spot any secondary damage that might have occurred due to a cut. This can thus, reduce the strength of the tire by several kilometers. 


  • Always get a professional tire repair shop to fit run-flat tires. Installing them on a standard mount may cause damage to the side or bead of the tire.  


  • Though the standard of RFTs after a puncture is approximately 90 km/hr for about 80 km, always remember that these are average values and taking advantage of the full potential may vary. 


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Types of RFTs


There are two types of RFTs - Self-Supporting run-flat tires and the Support Ring System.

  1.  Self-Supporting run-flat tires  



These tires have a sturdy and more solid sidewall that allows it to provisionally carry the weight of the car under lower tire pressure. This construction enables continued operation despite the loss of air pressure for a certain distance and up to a particular speed. These tires are also called self-sealing tire.


       2. Support Ring System



Some armoured vehicles manufacturers provide a support ring RFT systems that utilise a special rim of hard rubber or another structure to support the vehicle's weight in case of air loss. The internal support ring is, however, a less common design of run-flat tires.  


Advantages of RFTs


RFTs, whether the self-supporting RFTsor the Support Ring System, both come with a set of advantages that are stated below-



  • Mobility after a flat

Continued mobility is the biggest and most apparent benefit of RFTs. Even after being pierced by a nail or any sharp object, it allows the driver to continue driving to a safe spot and not halt the car in the middle of a busy road. 


  • Safety 

Aside from convenience, RFTs provide immeasurable protection as they allow staying safely mobile even after a sudden loss of air pressure.  


  • Stability 

In case of air loss or blowout, these tires continue to provide more endurance, which helps to maintain better control and manoeuvrability to the vehicle.


 Must Read : Can my existing car be armoured?




  • The topmost complaint of RFTs is that they are expensive. They are, in fact, around one-third time more costly than regular tires. 


  • As RFTs are heavier and thicker, they have an impact on the fuel economy by 1-2%. 


  • They are also harsher on the road and don't provide a lot of grip in low temperatures. 


  • Vehicles with these tires have no spare, which means they don't have a jack or other useful car tools. 


  • It is hard to tell if the run-flat tire is running low on air, because the sidewall is so stiff hence, thus making a tire pressure monitoring system an essential accessory. 


Despite its advantages, many automakers like BMW, Mercedes-Benz are offering them as a standard tire in some of their passenger vehicles mainly because of the risk of a tire being blown out after a puncture is practically zero.


For consumers too they are a good choice mainly because of two major advantages- safety and convenience, both rated high on the list of features they look for in a vehicle. 


Thus, after looking at the overall performance and credibility of run-flat tires and its various benefits, the time is not far when automakers will make them a prime choice for cars, as opposed to an exception in new vehicles. So, if you have RFTs in your car then do share your views in the comments belowabout your experience with these four disks and if they should become a standard choice of tires going forward.

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