How Self-regenerating Tire Tread Works

First, let's examine how tire tread wear happens, and why you need a self-regenerating tire at all.

Modern radial tires are comprised of a thick rubber outer layer over top of loops or belts of steel and polyester fabric. When these parts are assembled, the rubber part is initially totally bald, until a machine cuts deep patterns into the tire rubber called treads.

Why do tire companies put those grooves into the rubber? Why not just make the tires a bald, smooth surface? If the tires were totally smooth they would have no traction on slippery surfaces. For that reason, tires have tiny grooves and patterns on the outside surface that channel the water away from the contact patch -- where the rubber meets the road surface -- improving the tire's grip.

Different types of tires have different treads based on what kind of vehicle they're used on. Sports cars have very aggressive tire tread patterns because their top priority is handling -- as result of lots of wide grooves, the ride quality on these tires can be harsh. Luxury cars often use less-aggressive patterns because their goal is comfort and low road noise [source: Racerchicks.com].

The problem with tires is that they wear down over time. Subjected to water, heat, acceleration, and braking, the rubber on the tires is gradually shaved off with each use. Most tires have a wear indicator built into them that tell you when it's time for them to be replaced. Tire wear indicators vary from brand to brand, so it might be a good idea to contact your tire's manufacturer to find out exactly what to look for and where.

You risk your safety when you drive on bald tires. When a tire gets worn down, it can't function as well in wet conditions. It's also more susceptible to punctures and blowouts, and your handling and stopping distances are compromised, too. In addition, it's illegal in most states to drive on tires that have worn down to 2/32 of an inch (1.6 millimeters) or less of remaining tread depth [source: Tire Rack]. After a while, your tires need to be replaced. But what if there was a way for tires to last longer by having extra layers of tread that are revealed as the rubber wears down? Michelin found a way to do just that.

In this next section, we'll take a look at Michelin's self-regenerating tire model, XDA5, and examine how it extends tire life up to 30 percent.

To most car owners, 300,000 miles may seem like a huge amount to put on your vehicle's odometer, but for 18-wheeler trucks, that kind of distance is business as usual. It's also happens to be just about how long their tires typically last

[source: Brown].

These trucks can cover 1,000 miles (1,609.3 kilometers) in a single day and carry tremendous amounts of weight wherever they go. They're equipped with special, heavy-duty tires, but of course, those tires aren't immune to the laws of physics, either. The tires wear down over time just like yours do, and the cost of replacing tires adds up for trucking companies -- remember, they also have to pay the cost of running behind schedule while the tires are being replaced.

In 2007, tire manufacturer Michelin announced a new solution to the problem of tire life on big rigs. Their XDA5 tire is designed to give truck tires a 30 percent longer lifespan through the use of regenerative tread technology. Sounds awesome, but how does it really work? Essentially, as the tire wears down, the tread reveals new grooves and tread blocks. Once one set of tread has been worn away, a new layer arrives on the surface from underneath the worn out layer [source: Michelin]. The tread on modern tires is comprised of interlocking blocks of rubber. Michelin's XDA5 tires are molded with grooves concealed deep inside those tread blocks. The new grooves are exposed once the tire is about two-thirds of the way worn out.

Does the tire itself regenerate? Not really. But once the grooves that are vital to traction in rain and snow are depleted, a new layer pops up, providing proper grip until a new set of tires can be installed. The tires still get worn out, but they have new grooves, which mean they last longer.

The tires also contain technology called raindrop grooves -- sipes situated deep inside the tire that are designed to channel water on the road surface to the left and to the right, away from the bottom of the tire. This prevents slippery buildup underneath the tires. When the tread becomes worn, the channels gradually open to create new sipes in the middle of the tread block. Michelin says it uses a patented manufacturing technique to mold the XDA5 tires in three dimensions, creating grooves that exist underneath the surface of the rubber.

In the next section -- is 30 percent longer life really worth it? What are the benefits of self-regenerating tire tread? And will you be putting these tires on your family sedan anytime soon?

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Truck tires usually have grooves about an inch thick, and, for safety reasons, are typically sent for retreading when they've reached a depth of 8/32 of an inch (6.35 millimeters). This gets expensive for trucking companies, as the tires usually cost between $250 and $400 apiece -- and don't forget there are often as many as 18 of them on each truck [source: Brown]. Considering that the tires need to be replaced after about 300,000 miles, this becomes an expensive proposition for transporters, who may own hundreds of trucks that traverse the country day-in and day-out.

It's easy to see how a tire that lasts up to 30 percent longer can mean big savings for a trucking company. The self-regenerating tread tires cost about 6 to 10 percent more than an ordinary tire, due to the more complex manufacturing process.

Currently, these tires are only available on heavy-duty, 18-wheeler trucks. In other words, you won't be mounting these tires on your family car anytime soon. Why is that? Again, your family car just doesn't see the kind of punishment and long-distance hauling that these trucks routinely do -- and you don't have to buy huge amounts of tires in bulk for your fleet, either. When your tires get worn out, it just makes more sense for you to buy new ones, not have a high-tech tire that keeps going long after it's worn out.

Regenerating treads aren't the only way to make tires last longer. On the next page, we'll examine other tire-saving technologies, including ones that will keep you safer.

Over the decades, tires have changed much more than most drivers realize. Tire companies are constantly coming up with new ways to make tires that achieve better safety, handling, fuel economy and longevity. In fact, there are many ways to extend the life of a tire without Michelin's complex self-regenerating tire treads. Here are just a few examples of what's currently on the market:

Michelin offers some tires with its Infinicoil technology. This uses a giant steel cord -- up to 1,312 feet (400 meters) long -- wrapped underneath the rubber layer. The steel increases the rigidness of the surface of the tire, and allows them to be made wider than before. They also tend to last longer [source: Tire Review Online].

The same company also introduced a concept called the Tweel Airless Tire. This uses rubber tread supported by small, flexible spokes extending outward from the center of the wheel. It has no air inside, just flat rubber connected to the spokes.

A Czech company, Coda Development, has pioneered a system called the self-inflating tire (SIT). This keeps the tire pressure constantly at its proper level with a valve that takes in outside air and forces into the rubber. Once at optimal pressure, the valve shuts off the intake of air and circulates it inside the tire. Since improperly inflated tires can lead to blowouts and even rollovers in some circumstances, this technology, which always keeps the tires inflated to the right level, could mean big advances in safety [source: Coda].

All of those technologies are interesting concepts, but what's on the road that you can use right now? Don't forget about run-flat tires. Those have been around for more than a decade, ever since they came as standard equipment on the 1997 Chevrolet Corvette, and have been gaining popularity among performance and luxury car owners ever since. Self-supporting tires (SSTs) have heavily reinforced sidewalls that support the tire in the event of a tire puncture. One system from Michelin uses a semi-rigid insert inside the rubber to support the car in the event of a blowout [source: Edmunds].

However, run-flats have their tradeoffs as well. They're famous for having a harsher ride than normal tires, and in the event of a puncture, most are limited to a maximum speed of 50 mph (80.5 km/h) and a limited distance until they can be repaired or replaced. Many car companies have begun offering run-flats as standard equipment but not offering a spare tire or even the equipment required to change a tire. After all, if a run-flat tire can get you to safety when it's punctured, what's the point of carrying around a heavy tire iron, jack and spare tire?

For more information about tires and other related topics, follow the links on the next page.