Tire Physics Explains Why Cold Tires Destroy Your MPG

Rolling resistance is a way to measure how much energy your tires use as they roll down a street or highway. It's something you should always know. The factors that affect rolling resistance are the temperature of your tires, the speed of your car, the type of rubber compound used in the tires, and the tire pressure inside those tires. Rolling resistance is responsible for at least 20% and as much as 30% of your vehicle's fuel use in lower-speed driving. Generally speaking, a higher rolling resistance will lead to a poorer result in terms of fuel economy, which is why you should avoid tires with high rolling resistance if you drive an EV. 

The temperature of your tires typically progresses from cold before you start driving each day, to warm after you have been driving for a while. These temperatures have been measured as ranging from ambient temperature when cold to 127 degrees F during normal driving, going up to 145 degrees F on a longer drive. As your tires warm up, two things happen simultaneously — their rolling resistance decreases, and their inflation pressure increases as the air inside the tires expands. Both of these events reduce rolling resistance and improve your car's fuel economy, compared to cold tires.

Other factors that contribute to rolling resistance include the speed of your car and the type of rubber compound used in the tires. Higher speeds increase a tire's rolling resistance, especially if you are maintaining speeds higher than 50 mph. This causes a loss of energy within the tire, due to its viscoelastic nature, in which the tire acts as though it is both a solid and a dense liquid. Due to friction that occurs within the tire's rubber, some of its energy is converted to heat, which explains why tires get warm after they have been driven.

The type of rubber that your tires are made of also contributes to their rolling resistance. Thanks to advances in tire materials, many tires made for today's vehicles use silica to replace the carbon black that was previously used to make those tires. This has led to tires that both improve grip on wet surfaces and reduce rolling resistance, eliminating one of the many tradeoffs that tire engineers still have to make when creating tires for specific purposes. Buyers of eco-type tires prioritize fuel economy, performance tire buyers tend to value grip above all else, while touring tire buyers want a balance of performance and fuel efficiency. There are even some tires that must roll in a specific direction.

So, the next time you are shopping for tires, consider their rolling resistance along with the other factors that you value in a tire. While some markets have rolling resistance labeling requirements, the U.S. does not.