Understanding the relationship between gear ratio, wheel size, and cadence in cycling is crucial for determining speed and, with additional data like weight and distance, calculating the power needed. The gear ratio, which is the ratio of the number of teeth on the chainring to the teeth on the rear cog, directly influences how hard or easy it is to pedal. Wheel size affects how far you travel with each pedal stroke. Cadence, or the rate at which a cyclist pedals, is measured in revolutions per minute (RPM). 

By combining these factors, cyclists can estimate their speed. For instance, a higher gear ratio means more effort per pedal stroke but higher potential speed. When factors like the cyclist's weight and the distance to be covered are considered, it becomes possible to calculate the power output required. This knowledge is especially valuable for athletes who need to determine if they have the right gear set ("enough gear") or sufficient power to maintain reasonable cadences, particularly when climbing hills. This can lead to more efficient training and better performance.