Final answer:
A cyclist drafting off another at high speeds conserves energy by reducing the air resistance they face. This allows for a 27% energy savings due to the lead cyclist disrupting the airflow, which is significant as over half of a vehicle's power at highway speeds goes to overcoming air drag.
Step-by-step explanation:
A cyclist can conserve about 27% of his energy when riding at 25 mph by drafting off another cyclist due to the phenomenon known as air resistance or drag. When a cyclist rides behind another, the lead cyclist disrupts the airflow, thus reducing the air resistance the trailing cyclist encounters. This allows the trailing cyclist to expend less energy to maintain the same speed. At highway speeds, a substantial amount of power is used to overcome air drag, which is relevant to both cyclists and motor vehicles as indicated by research that shows over 50% of a car's power is used to overcome air drag at these speeds. Moreover, adopting the most fuel-efficient cruising speed is similarly beneficial for both cars and bicyclists, aiming to minimize air resistance and thereby conserving energy.