Pneumatic tires were invented in the 19th century and were quickly adapted to bicycles. Since then, better materials and manufacturing processes have improved performance and durability, but the general design, a durable rubber casing supported by pressurized air, has remained the same.
Most road bikes use clincher tires, which are held on the wheel by grooves in the rim. A separate inner tube is filled with air. Clinchers are common and inexpensive. Some road bikes use tubular tires, which consist of a tube sewn into a tire that is then glued to the rim. Tubulars can perform slightly better but are harder to maintain.
Modern road bikes use a tire size known as 700c. Older bikes might use 27-inch tires. These sizes are not compatible, but the 27-inch size is still stocked by most bike shops.
Thinner tires offers less rolling resistance, while wider tires absorb shock and resist punctures. The 700c tire widths are measured in millimeters, from 20 to more than 40. Heavier riders should consider wider tires.
A nearly slick tire offers the best traction on smooth, hard roads. Some amount of tread might be desirable for riding in sandy or muddy conditions.