Wheels and tires
Main article: Bicycle wheel
The wheel axle fits into fork ends in the frame and forks. A pair of wheels may be called a wheelset, especially in the context of ready-built "off the shelf", performance-oriented wheels.Main article: Bicycle tire
Tires vary enormously. Skinny 18 to 25 millimeters wide, road-racing tires may be completely smooth, or (slick). On the opposite extreme, off-road tires are 38 to 64 millimeters wide and usually have a deep tread for gripping in muddy conditions or metal studs for ice.Source : wikipedia