In most modern cars
In most modern cars aerodynamic drag begins to become significant above 40-45 mph. Tires consume approximately 20% of the energy that makes it to the wheels. When you buy tires get “Eco” tires. Avoid “all-weather” tires as their more aggressive tread consumes power. Inflate the tires to about 10% above the manufacturer specified pressure; it is a compromise between ride smoothness and efficiency. Excessive pressure will make the tires more bouncy than the dampers (“shock absorbers”) are designed to control. “All-weather” tires are a compromise between dry and wet pavement and snow. If you need snow tires put them on.