Low rolling resistance, high load capacity: tires for electric cars must have special talents. How is that exactly?
More and more manufacturers are marketing tires specially developed for electric cars. That may sound strange, because electric cars do not need special tires. Still, it makes sense, because such a tire can contribute to a reduction in power consumption and thus to an increase in the range. The emphasis is on low rolling resistance, which is why ‘electric tires’ often have large diameters and a narrow tread. Rolling resistance can also be reduced through the tread compound and tire structure. A conventional summer tire has a rolling resistance of between 7 and 9 kg / t. Eco tires or tires with low rolling resistance achieve values of 6.5 kg / t and less. How much profit in radius of action is this possible? “Reducing rolling resistance by 1 kg / t is expected to lead to a gain of three to four percent,” said Burkhard Wies, head of development at Continental. With a Renault Zoe with a range of about 150 miles, that would be 10 kilometers, while a Tesla Model S with a range of about 500 miles would achieve about 20 kilometers more.
Load Index
Another point of attention for tire manufacturers is that electric cars are quite on the heavy side and that electric motors always provide a lot of pulling power. Both factors can cause electric car tires to wear out faster than gasoline or diesel cars. That is bad news for the environment and for your wallet. “It is important to make a distinction here,” says Stefan Küster of tire manufacturer Kumho. “This higher tire wear plays a greater role in EVs that weigh more than two tons and have a lot of pulling power than, for example, with a compact Renault Zoe. In addition, the driver’s driving style is an important factor with regard to tire wear. ” How wear-resistant a tire is strongly depends on the rubber composition used. The regal weight of electric cars also places demands on the carrying capacity of car tires. When choosing, it is therefore very important to pay attention to the so-called load index. This can be found by dividing the maximum permitted weight of your car, which can be found on the registration certificate, by four and then looking in a table (available online) to see what the corresponding load index is. Of course, a good tire supplier or car dealer can also inform you about this. Needless to say, we also mention that the prescribed tire pressure must be respected and checked regularly; this of course has an influence on the load capacity and the wear of the tire.
Sound and safety
Because the electric motor is quieter than a combustion engine, tire noise is much more noticeable. Low-noise treads therefore have a major influence on the overall driving comfort. Vibrations in the tire cavity play an important role in noise development, as they are passed on to the interior. Foam inserts on the inside of the tire tread can absorb these vibrations. Such polyurethane sponges are now used by some tire manufacturers. Pirelli calls this solution Noise Canceling System, while Continental calls it ContiSilent. Another aspect is safety. Can a tire optimized for rolling resistance perform well in that area at the same time? “From a technical point of view, there is a conflict between the objectives of low rolling resistance and optimal grip,” explains Burkhard Wies. “When developing tires, a good compromise between both properties must be achieved, which is very successful thanks to advances in rubber compounds.” Stefan Küster agrees: “A tremendous amount has been achieved in the field of rubber compounds over the past two decades. As a result, it is now possible to produce an energy-efficient tire that also offers very good grip. ” Our conclusion: for many, the environmental factor is the center of attention when it comes to electric cars. Low rolling resistance is therefore an important point. At the same time, tires must ensure good grip and a short braking distance – of course also in the case of electric cars. Not all tire manufacturers are equally successful in accomplishing this balancing act. The EU tire label only provides an indication of this. Even more informative are the results of independent tire tests, as we regularly publish them, where you can compare how the tires in the different categories really perform.