Bicycle gears are essential for adjusting the bike's speed and ease of pedaling. The two main types are derailleur gears and hub gears. Derailleur gears use a system of levers and pulleys to shift the chain between different-sized cogs on the front and rear wheels, allowing for a wide range of gear ratios. This system is common in road and mountain bikes. Hub gears, on the other hand, are enclosed within the wheel hub, providing a more protected and low-maintenance option. They typically offer fewer gear options but are easier to use, making them popular for city bikes and commuters.