I get together with a few of my friends about once a month and discuss topics including sports, stock market, cars, technologies and travel—but no politics. In one such recent discussion, one of our friends made a statement about his new (about one year old now) toy, an electric vehicle (EV) from one of the popular brands. He announced with disappointment that tires on four wheels of his vehicle are worn out in less than 12,000 miles and need replacement, a costly affair. It suddenly took my interest, and that is what I want to discuss here.
One of the factors for tire wear is obviously vehicle weight, and we all know EVs are heavier than gas engine propelled vehicles. I explored deeper into it, and my findings are presented in Figure 1. I looked across different brands and different size vehicles and compared curb weight of gas-powered vehicles with comparable size EVs. The curb weight is the weight of a vehicle, including fuel and standard equipment while the gross weight of a vehicle includes passengers, luggage and cargo of any kind. So, curb weight reflects actual weight of a vehicle. I collected the data from vehicle specification in manufacturers’ and their dealers’ websites. So, there could possibly be a small discrepancy in numbers. Wherever possible, I picked the same vehicle model available in both gasoline powered and electrified versions. Particularly for EVs, I paid attention to all wheel drive (AWD) or rear wheel drive (RWD) configuration, because AWD includes an additional power unit in the rear consisting of an electric motor and gear unit, adding weight. It is to be noted that the battery pack is a significant contributor to curb weight of an EV.
Figure 1. Weight of selected electric vehicles compared with similarly sized gasoline-powered vehicles.
The data suggests that EVs are heavier than gas-powered vehicles by about 2.9 % to 33.5% with the average being 18.3%. Therefore, EV tires need to be more durable. An extensive material processing, design and engineering work goes behind the manufacturing of tires to balance several performance attributes, i.e., traction, handling, noise, wear (durability), load capacity, speed rating, etc., considering driving under different weather conditions. Generally, tire manufacturing starts with material selection. Tires are made out of natural rubber or synthetic rubber and mixed with carbon black, silica and plasticizers. These are essential components for manufacturing treads, the part of tire in contact with road surface. Therefore, tread compounds are critical for wear performance.
However, the trade-offs are rolling resistance and handling on wet pavement. Significant enhancement on one performance can lead to compromise on other performance attributes; therefore, all these attributes need to be optimized. Tire contour is another important design element for wear performance. A flatter tire provides better wear (because of less unit loading), handling performances and improved braking (less stopping distance) but compromises on ride quality, noise and rolling efficiency (fuel economy). Rolling resistance is particularly important for EVs because it impacts energy consumption and, thus, battery charge interval.
Design and manufacturing of tires with optimum performance attributes involve complex engineering. Tires used for traditional gasoline-powered vehicles are probably not the best for meeting additional performance requirements for EVs. It seems more research and investments are necessary for making tires for EVs more durable.
Dr. Arup Gangopadhyay is retired from Ford Motor Co. and is based in Novi, Mich. You can reach him at arup.gangopadhyay@sbcglobal.net.