Final answer:
A car's tires need more air in the winter because the air inside the tires contracts with lower temperatures, leading to reduced tire pressure that must be corrected for safety and performance. The correct answer is The temperature is lower, so the air inside the tires contracts.
Step-by-step explanation:
A car's tires need more air in the winter than they do in the summer primarily due to the relationship between temperature and pressure for gases, which is described by the combined gas law. In colder temperatures, the air inside the tires contracts, leading to a decrease in tire pressure.
This is why you often have to add air to tires in the winter. As the temperature drops, the air inside contracts, causing a lower tire pressure than in warmer conditions. It's essential to maintain the right pressure for optimal tire performance and safety. Tire pressure is best measured when the tire is cold, as driving the car heats up the air inside the tires, increasing the pressure. Most manufacturers specify optimal tire pressure for cold tires.