According to Bicycling.com, the average bike speed is between 9 and 18 miles-per-hour (mph). However actual speeds will depend on the rider's ability, the terrain, and the riding conditions.
When riding down a hill, speed can increase to 20 mph or more, but when climbing a steep incline, that rate will decrease significantly. Keeping average bike speeds in mind is useful for someone who is training to become an above-average cyclist. To improve speed, it is recommended that a rider focus on technique, endurance and leg strength. This can be achieved with weight training and/or by riding on an incline of 5 percent.