Wheel sizes refer to the diameter of a wheel, typically measured in inches. Common sizes for bicycles include 26-inch, 27.5-inch, and 29-inch wheels, while cars often use sizes like 15-inch or 17-inch. The size affects the vehicle's performance, handling, and comfort, with larger wheels generally providing better stability and smoother rides over rough terrain. In addition to diameter, wheel width is also important, as it influences traction and grip. Wider wheels can offer better stability and control, especially in off-road conditions. Understanding wheel sizes helps users choose the right equipment for their specific needs, whether for bicycles, cars, or other vehicles.