Experienced bicycle riders know that fatigue comes from how hard you press on the pedals, not how fast you turn them. Novice racers may try to ride with maximum force on the pedals, but they quickly exhaust themselves and often can't even finish the race.
Cycling is a power sport. The number of times you spin your bicycle pedals in a minute is called your cadence, and your power is the product of the force that your feet apply to the pedals time your cadence. A study from Toledo, Spain shows that spinning the pedals too fast slows you down ( Medicine and Science in Sports and Exercise, May 2006). Most bicycle riders do best when they chose gears that allow them to pedal at a cadence of 80 to 90.
You want to pedal as fast as you can with the greatest force you can maintain on your pedals, but if you spin too fast, your brain cannot coordinate your muscles so you lose efficiency. Try to choose gears that allow you to spin as fast as you can and still feel some pressure on your pedals. If you have to push on your pedals so hard that your body moves from side to side, you need to reduce the gear ratio and pedal faster. If you are spinning faster than 100 times a minute, you are probably losing coordination. Bicycle computers that show your cadence are available in bike shops and online bicycle catalogs.
When you are going out on a long ride, try to keep a comfortable fast cadence. However, if you are going to sprint or race for less than 30 minutes, you will ride faster by putting more pressure than usual on you pedals, which will slow your cadence by about 10 percent. You can also use this technique to pick up the pace when you want to catch up with another rider.