In cycling, the gear ratio, determined by the number of teeth on the chain ring and sprocket, combined with the cyclist's cadence (pedaling speed) and the wheel diameter, dictates the bike's speed. A higher gear ratio means covering more ground per pedal stroke but requires more effort, while a lower ratio makes pedaling easier but covers less distance. This understanding is essential for cyclists to select the most efficient gear for various terrains, ensuring optimal performance and endurance.