A leisurely bike ride of 10 mph or less will burn fewer calories than cycling faster in a 20-minute period. A 150-lb. person biking at less than 10 mph will burn 90 calories in 20 minutes, according to the Calories Burned Biking website. By increasing the speed to 12 to 14 mph, that person will burn 198 calories in 20 minutes. A 200-lb. person will burn 120 calories with a leisurely bike ride, but traveling between 12 and 14 mph will burn 264 calories in 20 minutes. A 240-lb. person will burn 144 calories in 20 minutes, while more vigorous biking will burn 317 calories.