What is different about the tires on an EV?
We always say that EVs are just like traditional cars - only better. However, there are special considerations with EV tires that even the most seasoned electric drivers may not know about.
If you're curious how tires affect your EV's efficiency, look no further than rolling resistance. What is this science-sounding term?
For any car, tires are the thing that makes contact with the road, and wherever they do, there is friction between the rubber and the blacktop. Friction is a loss of energy - the same energy that should be making your car go. While tire friction, or rolling resistance, is present in any car, it makes much more of a difference with an EV because of how efficient electric motors are. According to Russell Shepherd, a technical communications director for Michelin,
“tires eat up about 5 percent of the energy an ICE vehicle generates. But in the more streamlined EV drivetrain, tires consume about 16 percent.”
This makes rolling resistance an obvious place to save energy and EV tire makers consider their solutions the "secret sauce" of their products.
The antidote to rolling resistance is to reduce the friction between the tire and the road. But, if you reduce the friction too much, the car can't grip the road and you can skid, slide, or spin out. This is especially true with the rapid acceleration (“flooring it”) that makes EVs so fun. Each car manufacturer and driver can select tires that prioritize traction or range. For instance, performance EVs that are built for speed tend to have tires with greater rolling resistance so their drivers can gun it, while more sensible EVs might prioritize a lower rolling resistance to increase range.
Speaking of fast acceleration, we come to torque. This is what generally makes cars “fun to drive.” It’s certainly what makes EV drivers want to floor it at every stop light.
Torque is the rotational force that a motor (or engine, in an ICE) produces and it goes to turning the tires - and moving the car. More torque leads to faster acceleration. In an ICE, maximal torque occurs at a specific rotational speed (RPM), so you have to get “up to speed” to experience this torque. In an EV, there is only one gear and much less mechanical stuff that delays getting the electric energy to the wheels. There are a lot of technical details we’re skipping, but the takeaway is that EVs can get maximum torque from a standstill, while an ICE needs to get to the correct RPM first.
If you've ever accelerated in an EV, you probably know what we're talking about.
This zero RPM torque makes a car fun to drive by giving it a responsive and peppy feel at low speeds. But it should be no surprise, then, that flooring your EV frequently will wear down your tires faster than a gentle acceleration. This is because of torque. EV tires tend to be made of more resistant material than tires for combustion cars.
PS - the same factors are at play with the “reverse torque” your wheels experience with regenerative braking.
EVs are far heavier than their ICE counterparts (at least 10%). Since tires are the thing that separates the car’s body from the road, they are impacted by the extra weight. You could distribute that weight by making the tires wider, but that would increase the air resistance of the vehicle and drive down efficiency. Instead, many EVs come with “heavy duty” tires made of extra-stiff material and require tire pressure to be much higher than in an ICE. I was shocked the first time I checked the tire pressure on a Tesla and saw that it was supposed to be 45 PSI - 20% higher than the ICE I had driven previously. The extra air pressure cushions the EV cabin from the road. And, you’ll probably need to refill your tires with air more often than you do with an ICE. It’s worth doing, since it really helps with efficiency. Most manufacturers recommend checking EV tire pressure monthly (or whenever temperatures fluctuate a lot).
Drivers love that EVs are silent, but a lack of engine noise can mean that you hear the tires on the road, and ruin the serenity and peace of the ride. This is especially true on hard concrete or rough roads. Tire manufacturers are engineering a quieter ride by adding acoustic dampers or foam into EV tires. Since these materials can make tires stiffer, it’s worth noting that prioritizing silence may trade on traction.
Ian Coke, director of quality at Pirelli, talks about the options to design a quiet tire: "there's a variety of technologies out there. [Tread] pattern is one aspect. There has been a big uptake in noise-cancellation systems, which [involves] an open cell structured foam [being] placed inside the tire; the sponge absorbs the noise, and [the noise cancellation] stops it from being carried through,"
What is special about EV tires?
Nowadays, there is a whole new set of specialty EV tires that are meant to optimize these special considerations for electric cars. They are built to handle the added weight and torque while muting road noise. However, the requirements for a good EV tire can be at odds with each other. You want low rolling resistance to maximize range, but need traction in order to enjoy the performance of your zero-RPM torque. You want to buffer the sound of the tires on the road, but also ensure longevity. It’s not a simple problem, and tire companies are racing to the finish line with proprietary optimizations.
How does changing your tire affect your range?
Michelin product manager Steve Calder explains that “there can be about a 6 percent change in range between when the tire is new and when the tire's at the end of life.” And, depending on your specific needs, you may opt for a tire that prioritizes some features more than others.
For instance, Russell Shepherd elaborates on the effect of rolling resistance on range. In the EU, tires come labeled with a rolling resistance rating, and the difference between Michelin tires with the most and the least resistance can translate into a 15% difference in range. In general, a 20% increase in rolling resistance means a 5-8% loss of range. Another calculation puts the range difference between low rolling resistance and performance tires at around 50 per 200 miles - that’s 25%!
What about tire size?
The rule of thumb is that wider tires provide better traction and handling, since there is more contact between the wheel and the road. However, this can also cause range losses through drag and friction.
Related, is how wheel size affects range. As demonstrated with Tesla wheel sizes, range generally drops with larger wheels.
Here are some tips to keep your tires in good shape for as long as possible:
- Check alignment - this is a frequent issue, especially with Teslas. If your tires are wearing unevenly or faster than seems reasonable, it’s a good first step.
- Check pressure - since EV tires are so heavy, they need all the PSIs the sticker says. Even a slight lack of tire pressure can affect rolling resistance, leading to range loss. However, be careful overfilling your tires to game range. This can lead to a lack of traction, especially on wet or icy roads.
- Rotate tires - Tesla recommends every 6,250 miles
- Performance tires tend to be softer to “grip” the road more, but they will also wear down faster.