How Are Self-Sealing Tires Different From Run-Flats & Do They Really Work?

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Getting a flat tire while you are driving can be a very dangerous and frightening experience. Over the years, three different technologies have emerged to make sure that you can safely keep motoring, even if a tire is compromised. These are self-sealing, run-flat, and airless tires. While airless car tires are just coming onto the market, seal-sealing and run-flat tires have been available for decades while still undergoing improvements.   

There's a misconception in some corners of the Internet that self-sealing tires are a type of run-flat tire. While both run-flat and self-sealing tires can help you keep moving after your tire gets poked, they work in different ways and need different technologies to make them work well even before any accidents occur. Self-sealing and run-flat tires also handle different types of problems, so if you are looking to upgrade the safety of your ride, you'll have to take this into consideration.

Unlike self-sealing tires, run-flat tires do not need air inside to be able to keep the car moving. The sidewall of a run-flat is designed to support the car in motion for a specific amount of time. Passenger car tires, such as the Perilli Zero sold on Amazon, are capable of being run at 50 mph for 50 miles before losing their structural integrity to the point that they become unusable. Most run-flat tires are designed with a tread puncture in mind. 

Run-flat tires are often used as a component of a bulletproof tire system along with an auxiliary device, usually rounded blocks, that attaches to the wheel inside the tire. Military-grade run-flats are expected to be able to take bullets to the sidewall as well as the tread, though in civilian life, tread face punctures are the main concern.

Manufacturers such as BMW have been selling their cars with run-flat tires instead of spare tires for years. In this way, they save on the space, weight, and expense of having to equip the car with a spare. 

Self-sealing tires are designed to keep air in them under conditions that would lead a normal tire to deflate. Unlike run-flats, the sidewalls are not designed to hold the tire up without inflation, and unlike tube tires, there is no separate inner tube to hold the air in. With the latest self-sealing tires, there is an extra viscous layer on the inside of the tire that closes the gap where the tire was punctured and seals the hole. 

Self-sealing tires often do not have sealant on the sidewalls, so they are at their best if the tread is compromised. There are limits to their ability to handle holes over a certain diameter. This means that if the puncture is large, you might have to change the tire where a run-flat would let you keep going. If the puncture is within the tire's specifications, though, you can keep driving at normal speeds, which you won't with a run-flat. The ride is also better than with a run-flat, though that is changing.. Moreover, under normal operation, you can see if the tire is inflated or not, instead of relying on a sensor as in the case with a run-flat.  

Michelin invented the self-sealing tire in 1935, and the technology behind them has kept developing. Continental and others have developed coatings that can seal holes from multiple objects without affecting the internal pressure. Tyre Reviews managed to put a GoPro inside a tire and record nails entering the inside of the tire and leaving, while the tire stays inflated. 

The video shows that self-sealing tires do work, and that they do offer some advantages over run-flats both in everyday operation as well as when something goes wrong. Both types of tire are put on new cars these days, and Ford has been putting Michelin Self-Seal tires on some Explorer models since 2020.

Self-sealing tires do have some limitations compared to run-flats in that a hole in the sidewall is unlikely to be sealed, whereas a run-flat can handle holes in the sides. Also, a run-flat can handle larger punctures in the middle of the tread because the sidewall holds the tire up, while self-sealing tires are limited to 1/4" or so. On the other hand. ride quality, especially over rougher road surfaces, can be better than run-flats, as the load-bearing profile of a self-sealing tire is essentially the same as a regular tire. As the videos show, both run-flat and self-sealing tires do work, and both are proving themselves to be safer than regular tires.