The Silent Innovation Behind EV TiresThe Silent Innovation Behind EV Tires

When considering the refined and whisper-quiet experience of an electric vehicle (EV), the role of tires might seem secondary. Often overlooked, tires have a profound level of influence over the performance and ultimate function of any vehicle. For example, in the context of internal combustion engines (ICEs), performance attributes have been focused on increasing lateral grip thresholds, braking performance, speed ratings, etc. These are important parameters for any tire. However, applications on electric platforms require a host of other considerations.

The Impact of No Wait and Added Weight

One of the more distinct platform separators between legacy ICE powertrains and their electrified counterparts is the immediacy of power delivery. In an electric vehicle, previous mechanisms or characteristics found in ICE architectures such as “power bands,” “torque curves,” or even multi-speed transmissions are often absent. Instead, torque delivery is near-instantaneous, providing the driver with 100 percent of available torque at the flick of a switch (or accelerator pedal), bringing an entirely unique experience to not only the driver but the tires as well.

Factor in the weight of lithium-ion battery packs, and you have a vehicle that weighs up to 30 percent more than its gas-powered kin. On standard tires, this could increase premature wear by as much as 20 percent faster than bespoke EV fitments.

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Solving for weight and power delivery certainly requires careful consideration towards compound material selection to address high friction entry points, structural integrity solutions to account for the added weight, and the last and perhaps most distinctive platform nuance: EVs are very quiet.

It’s What’s on the Inside that Counts

Without the constant soundtrack provided by a traditional vehicle’s engine (usually about 50 percent of the cabin-related noises experienced), road-going feedback goes from a quiet backup singer to your lead vocalist carrying a less soothing tune titled “tire drone.” Excessive road noise can also become a distracting and fatiguing element for both driver and passenger, prompting tiremakers to put on their own R&D montage to build new products for new platform challenges.

Providing foundational support for the increased weight and power delivery profile, automakers are turning to new materials to help strengthen the structural integrity of EV tires. One such material is Aramid fiber. With a strength rating five times greater than steel, Aramid fiber is known as one of the world’s strongest fibers and when applied as a reinforcement layer, helps limit tire deformation at speed and provide more event ground pressure dispersion to limit tire wear.

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One of the more exciting developments to come out of said R&D efforts is the introduction of noise-absorbing foam material inside the tire’s carcass to dampen internal tire vibrations, or what’s known as “cavity resonance.” Cavity resonance is the phenomenon where the air inside a sealed structure, in this case, a tire, vibrates in response to outside forces, i.e., road imperfections, creating sound waves that amplify and echo within the tire’s hollow cavity. This same principle can be observed if you were to dribble a basketball or even more so with a larger yoga ball.

Hankook Sound Absorber technology. HANKOOK TIRE AMERICA CORP.

As seen in the graphic above, the technology found in our Hankook Sound Absorber application consists of lightweight open-cell polyurethane foam that lines the inside of the tire. When applied, the foam’s open-cell structure acts like a sponge for sound waves, reducing the amplitude of the sound waves as they pass through it, providing a reduction of up to 9 dB in cavity noise—a big lift when considering the earlier absence of engine-driven noise.

In terms of material selection, polyurethane’s low density makes it an ideal solution in EV applications with minimal weight additions and energy retention, both crucial considerations when factoring available battery ranges in addition to comfort.

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A Quiet Chorus

Keeping with the band analogy, if our sound-absorbing foam material were our star performer, the various tread pattern innovations would be our string duo, providing rhythm and harmony.

In conventional tread patterns, tread blocks (sipes, grooves, channels, etc.) are evenly distributed across the tire’s entire contact area. This creates a consistent noise pattern that can lead to more pronounced road feedback (tire drone) detection while driving. Instead, new methods such as “multi-pitch sequencing,” which involves varying the size and arrangement of tread blocks in a pattern sequence. This integration works to disrupt those road-generated noise frequencies along with the added performance in wet and dry road conditions. 

The final instrument in the EV ensemble deals with the air outside of the tire. While solving for cavity acoustics in the previous section, the air moving between a tire’s treads can also be a source of road noise and unwelcome disturbance while in the comfort of the vehicle. The solution comes by way of “Knurling Technology” (pictured below), which is applied with the tire’s grooves, narrowing the path of air and thus minimizing the noise without compromising the capabilities of the tire.

Hankook Knurling Technology. HANKOOK TIRE AMERICA CORP.

Setting New Sound Standards

Much like the technology in EV platforms themselves, tire innovation has progressed considerably since its first iterations. What were once derivative constructions or spin-offs of established ICE-led designs have evolved into something completely new. It’s exciting to see what new material advancements are still ahead as EVs and their specialized tires work in concert to redefine what peace and quiet can mean behind the wheel of a car.