19 aoû 21

Low-rolling-resistance tyres to increase EV performance

Even though the pandemic caused overall car sales to decrease by 16% worldwide in 2020, EV car registrations jumped 41% in the same year, meaning that there were 10 million EVs on the roads at the end of 2020. In the first half of 2021, registrations of EVs totalled 2,65 million, representing a +168% leap compared to 2020.

An increase in demand means an inevitable change in tyre production due to significant differences between fossil-fuelled and electric cars. The critical difference appears as weight, as EVs are generally 20% or 30% heavier than conventional cars due to the heavy batteries they are carrying. For instance, a Tesla Model 3 sedan weighs 1587kg while the Honda Civic sedan is 1315kg.

Another important characteristic of EVs is that they produce higher torque, reaching maximum torque from 0 rpm through an electric current in the engine that moves through a magnetic field and creates the twist creating the rotational force.

At the end of the day, higher weight and torque put more pressure on tyres, impacting the design of EV tyres that has a crucial effect on the range.

What are the main challenges of EV tyres?

Electrification of cars offers advantages such as lower emissions and maintenance costs while creating weight, torque, noise and vibration and range problems. EV tyres are less durable than traditional tyres and wear out 20% faster. Additionally, EV tyre design is crucial for energy consumption which can yield an additional 20% range. Not only 20 to 30% of fuel consumption of the car is related to tyre performance, but past studies revealed that 24% of CO2 emissions of a car depends on tyres.

To overcome these issues, manufacturers are shifting their focus on “low-rolling-resistance” as rolling resistance represents up to 20% of a car’s energy use.

Most of the EV tyres today are sold in XL sizes to be able to carry higher loads. Similarly, Pirelli announced a “high-load index tyre” for hybrid cars and SUVs that aims to handle 20% more weight than traditional tyres. Continental is working on a design to balance high instant torque with high tyre wear while focusing on the optimal grip to meet the longer braking distance caused by the increased weight. Michelin plans to lower energy costs while keeping other aspects such as wet grip and range. As a part of the new tyre design process, Michelin aims to manufacture all tyres with at least 40% sustainable materials by 2030 and making it 100% by 2050.

The most critical detail: range

With over 200 variables from tread design to the manufacturing process, the structure of EV tyres will be critical for providing an adequate range. One important example is the aero wheel Tesla used on Model 3 which has improved the efficiency by more than 3%, adding almost 16 kilometres of range.

Calculations showed that specialised low-rolling-resistance tyres may offer huge range penalties, as range capacity between them and less-efficient high-performance tyres may reach up to 85 kilometres in 320 kilometres.

Eventually, car manufacturers will also consider which tyre to choose or join forces with tyre manufacturers as the Volkswagen ID.3 hatchback will be equipped with tyres exclusively produced by Bridgestone.

Photo copyright: Shutterstock

Author: Müfit Yılmaz Gökmen