A smooth tire will have the greatest contact area and the best grip on a hard surface. Unfortunately it will also be most prone to hydroplaning. On a regular vehicle that has to be able to travel in any weather smooth tires can't be used, but bike tires are narrower and better at cutting through the water to the surface below so they don't need much treads to do OK in rain.
Road bikes have thin tires because they are operating on smooth surface and should be light.
If you want traction you need the tread. Smooth tires are only used for racing.
tire tread is for better traction on slippery surfaces smooth tires are for racing at hi speed
Cyclocross bikes are designed for off-road racing with features like wider tires, disc brakes, and more durable frames. Road bikes are built for speed on smooth pavement with lighter frames and narrower tires. These differences impact performance by making cyclocross bikes better for rough terrain and road bikes faster on pavement. Cyclocross bikes are more versatile for different terrains, while road bikes excel on smooth roads.
to move easily on rough suface like roads etc...
Bikes styles all have different tires to suit terrain. There are road racing tires, cruising tires, off-road tires and many different wheel sizes too.
On a smooth surface the best traction and lowest rolling resistance is had from smooth tires. On an uneven or soft surface, like mud and sand a treaded tire offers the best traction, and the poor rolling characteristics is a trade of you have to live with.
Cyclocross bikes are designed for off-road racing with features like wider tires, more clearance for mud, and disc brakes. Road bikes are built for speed on smooth pavement with thinner tires and a more aerodynamic frame. These differences make cyclocross bikes better for rough terrain and road bikes better for fast rides on paved roads.
Hybrids, Dutch AKA City bikes, A rigid MTB with smooth tires.
Road bikes have thin tires because they reduce rolling resistance, making it easier to ride faster and more efficiently on smooth roads. The thin tires also help to reduce the overall weight of the bike, making it easier to accelerate and maneuver.
Everybody that races dirt bikes "started" racing dirt bikes at some point.
yes haro makes a big range of racing bikes