The wheels on adult bikes are typically between 26 and 28 inches, but some are much smaller. Some adult bicycle wheels are as small as 16 inches in diameter. Smaller wheels change the way a bike handles, providing both advantages and disadvantages. Along with the size and position of the fork, handlebars, frame and other components, the wheels determine the performance and comfort of the ride.
Small wheels are a useful space-saving feature of many utilitarian bicycles. Collapsible bicycles used for commuting almost always have small wheels. These wheels keep the bike very small and allow it to be folded into a compact configuration. Small front wheels are used for specialized bikes designed for getting groceries, leaving more space above the wheel for cargo.
In many high-performance bikes, one or two small wheels allow the bike to go faster or perform better in its assigned role. Bikes used in time trials have a smaller front wheel which puts the rider in a lower position for better aerodynamics. Small front wheels on track bikes allow the rider to follow other vehicles more closely, using their draft to pull him forward. Small wheels are also used on BMX bikes, allowing the bikes to steer precisely and accelerate quickly.
Personal preference plays a large role in the size of the bike's wheels, and racers typically have a range of styles available to them. Wheel sizes offer a complicated trade-off. On the one hand, smaller wheels have a lower rotating mass, which makes them accelerate more quickly and turn with less force. Smaller wheels are also usually more aerodynamic, which cuts down on wind resistance. On the other hand, small wheels need to rotate more quickly, which produces more friction at the hub, requiring more work. Small wheels are less stable and generally provide a rougher ride, which can be a disadvantage over the long haul.