Market and product

The Problem with Pneumatic Tires

Modern tires operate on a simple principle: compressed air inside the tire supports the vehicle’s weight. This principle has been used for more than 130 years since the invention of the pneumatic tire in 1888. However, dependence on air comes with several inherent limitations.

Tire pressure must be checked regularly and adjusted according to seasonal conditions. Tires can suddenly puncture when encountering sharp objects on the road. Low pressure reduces fuel efficiency and affects vehicle handling. In addition, damaged tires generate a significant amount of waste - global estimates exceed 1 billion discarded tires annually, with South Korea alone producing approximately 370,000 tons of waste tires in 2022.

A Completely Different Structure

Non-pneumatic tires (NPTs) - also called airless tires - solve these problems by eliminating air entirely from the tire structure. Instead of relying on air pressure to bear loads, airless tires use a spoke system made from elastic materials, typically polyurethane, to support the vehicle’s weight and absorb shocks from the road surface.

The circular shape rotating around the axle remains unchanged, but the structure between the wheel rim and the tread is completely different. The spokes simultaneously carry loads, absorb impacts, and restore their original shape after deformation. Because there is no air inside, the tire cannot go flat or burst, and no periodic pressure maintenance is required.

Origins in Space

The first practical application of airless tires was not on Earth, but on the Moon - an environment where pneumatic tires could not function at all.

In 1970, the Soviet Union’s unmanned lunar rover Lunokhod 1 landed on the Moon with eight airless wheels consisting of metal rims supported by steel wire spokes and wire mesh treads. This structure was chosen because of the lunar environment: temperature differences between day and night could reach 300°C, there was no atmosphere to dissipate heat generated by friction, and no possibility of repairing damaged tires.

Between 1971 and 1972, astronauts of Apollo 15, 16, and 17 used the Lunar Roving Vehicle (LRV), equipped with four airless wheels made from 0.84 mm zinc-coated steel wire and measuring 81 cm in diameter. The vehicle reached speeds of up to 18 km/h and operated during multiple exploration missions.

On Mars, the rovers Sojourner (1997), Spirit and Opportunity (2004), Curiosity (2012), and Perseverance (2021) have all used airless tires. Opportunity operated for 14 years and traveled a total of 45.2 km - 57 times longer than its original design lifespan. NASA is currently researching superelastic tires made from nickel-titanium shape-memory alloys for next-generation exploration vehicles.

Applications on Earth

The idea of airless tires for automobiles first appeared in 1938, when American engineer J. V. Martin introduced a safety tire design featuring X-shaped spokes. However, serious development for passenger vehicles only began in the 2000s.

Hankook Tire began researching airless tires in 2010 and introduced the first iFlex prototype at the Busan International Motor Show in 2012. In 2015, the company unveiled a urethane-based airless tire capable of being mounted on mass-produced passenger cars and tested at speeds of 130 km/h.

Today, airless tires are already used in practice on several types of vehicles, including bicycles, golf carts, forklifts, and specialized vehicles. For conventional passenger cars, however, the technology is still in the development and testing stage.

Designs for Military and Autonomous Vehicles

Two of the most actively explored applications today are military vehicles and autonomous vehicles.

For military vehicles, the main requirement is continuous operation even if the tire is damaged. Hankook’s iFlex 2, introduced at DX KOREA 2022, features a dual-arch structure: the outer arch absorbs impacts from rough terrain, the inner arch reduces vibrations transmitted to the vehicle body, and both are connected through a hinge mechanism that maintains structural stability. The tire was tested on Hyundai Rotem’s HR-Sherpa unmanned multipurpose vehicle.

For autonomous vehicles, airless tires address a specific weakness: self-driving vehicles do not have a human driver inside to respond to sudden tire punctures. The iFlex tire presented at CES 2022 uses a multilayer interlocking spoke structure inspired by biological cell architecture, combining hexagonal and square shells with different stiffness levels to distribute loads efficiently. The tread features a hexagonal cell structure optimized for zero-radius turning maneuvers used by autonomous vehicles.

Materials and Recycling

One notable technical feature of modern airless tires is the use of uni-material construction. Instead of combining multiple materials such as synthetic rubber, carbon black, and metal as in conventional tires, polyurethane airless tires can be manufactured from a single material type. This simplifies the production process and improves recyclability after use.

Source: Hankook Tire & Technology (hankooktire.com)