Electric vehicles are notoriously quiet. You might think near silent operation would be a universally agreed upon good thing, but when the internal combustion engine is removed from the equation, a new issue arises.  

As it turns out, gas engines do a good job of covering up the noise a car’s tires generate. According to Hankook Tire, 50% of the noise in a vehicle with an internal combustion engine comes from the powertrain and just 30% comes from tire noise. With an EV, however, the powertrain only accounts for 15% of the noise you hear, while your tires are elevated to the dubious distinction of contributing the most noise, some 40%.  

This greater exposure of tire noise to the driver and passengers in an EV is why tire manufacturers have had to throw out the rule book and develop completely new solutions for electric vehicles. Hankook Tire has put a ton of resources into the research and development of its iON line of EV-specific tires.  

iON tires are an upgrade over traditional tires in nearly every way. They’re specifically designed to overcome the four main challenges an EV presents: tread life, rolling resistance, grip, and, of course, noise. When it comes to tread life, EV tires have to be much stronger because EVs weigh, on average, 30% more than ICE cars. Low rolling resistance, meanwhile, increases an EV’s efficiency, and therefore its range. Grip, the opposite of low rolling resistance, is also important because electric motors generate so much torque; without it EVs would lay smoky burnouts at every stop light.  

And then there’s noise. What is tire noise exactly? It’s not just the noise of your tires and the road touching at high speed that you hear through your car window. In fact, most of the tire noise you hear is coming through the components of the car itself to reach you.  

When your car’s in motion, the air inside your tire is vibrating, and the frequency of the vibration increases the faster you go. This is called resonant sound, which travels from your tires into the car’s axles. The axles, in turn, support the whole vehicle. Resonant sound is what you both hear and feel from your seat inside the car. 

Increased tire noise isn’t just annoying, it can also be unsafe. That constant drone and vibration can increase fatigue in a driver, especially during long trips. That’s why the justification for reducing the effect of tire noise while driving an EV isn’t just comfort, but also safety. 

Hankook Tire decided to tackle this challenge with a Shock and Awe approach, attacking it from multiple angles to achieve a 29% total reduction in noise with its iON evo AS tire compared to a regular tire. From the tread pattern to the rubber’s thickness to the use of sound absorbing materials and more, Hankook Tire has left no stone unturned in its search for precious decibels. 

Perhaps the largest factor that contributes to a tire generating resonant sound is its tread pattern. There are lots of different tread patterns out there, each designed for a specific purpose. These include such patterns as symmetrical V-grooves, zigzag, deep grooves, and even tires without any grooves in the case of slick tires used by race cars.  

The tread patterns used on iON tires employ several nifty tricks to minimize resonant sound. One is the use of lateral grooves called knurling within the main vertical grooves of the tire. These small lateral grooves are responsible for decreasing tire noise by nearly 1 decibel.  

Likewise, the side grooves on iON tires widen as they reach the edge of the tire. Hankook Tire engineers discovered this has the effect of both lowering the pumping sound a tire makes as well as increasing water drainage while driving in the rain. 

One particularly interesting trait of iON tires is their chamfer technology. The grooves cut to make the tread pattern of regular tires are usually done at right angles, so there’s the wall of the groove that directly meets the floor of the tread. iON tires use a chamfered cut that connects the wall of the groove to the tire floor with two smaller angles, which reduces noise during sudden stops. 

Hankook Tire

Hankook Tire

Lastly, Hankook Tire uses a sound absorbing material inside its iON tires, but it doesn’t stop there. The effect of that material is enhanced by changes the company’s engineers made to the tire’s stiffness, mass, and frequency.  

The increased stiffness of iON tires plays an important role. For one, it helps the tire better support the increased weight of EVs due to their battery packs. Regarding tire noise, though, it prevents deformation of the tire, which in turn prevents deformation of the air inside the tire, a contributing factor to the generation of resonant sound. 

Likewise, the mass of a tire contributes to the amount of resonant sound it generates; the more mass, the more noise is created. iON tires contain a higher percentage of natural oils, which improves their durability. Because of this increased resistance to wear, they need less material than conventional tires for the same overall mileage, which reduces their overall mass. 

Finally, we come to the sound-absorbing material itself. iON tires have a polyurethane sound-absorbing foam attached to their inner liner. This material alone accounts for a whopping 9.2-decibel reduction in resonant sound.

Of course, it doesn’t matter how good the iON line of EV-specific tires is if there isn’t a set that fits your car and the conditions in which you drive it. Hankook Tire really excels here, offering iON tires across 7 separate product lines: 
 

  • iON evo AS: all-season performance tire for passenger cars and SUVs 
  • iON evo: summer sport tire for passenger cars and SUVs 
  • iON i*cept: alpine winter studless tire for passenger cars and SUVs 
  • iON FlexClimate: all-weather performance tire for passenger cars and SUVs 
  • iON Nordic ice: nordic winter studded tire for passenger cars and SUVs 
  • iON GT: summer touring tire for passenger cars and SUVs 
  • iON ST AS: all-season touring tire for passenger cars and SUVs 

And Hankook Tire is adding more sizes to the iON line every day. The company plans on adding 49 more sizes by the end of 2024, bringing the total count to 259 sizes. There should be an iON tire that fits every electric car, truck, and SUV on sale in America. 

When you take away the noise of an engine and replace it with electric motors, what used to be a distant purr becomes a roar right in your ears. It’s one of the maddening paradoxes of EV ownership – less engine noise equals more tire noise – but Hankook Tire has developed the answer with its iON line of EV-specific tires. Grab a set today so you too can enjoy the serene driving experience that EVs promised but haven’t delivered… until now. 

Got a tip for us? Email: tips@insideevs.com