Vehicles come in many shapes and forms, and they each use different technologies to operate efficiently. For instance, cars and buses that travel on roads use rubber tires, while trains and subways that run on tracks use metal wheels. The reason behind these different choices comes down to one crucial factor: friction.

What Is Friction? 

Friction is the force that occurs when two surfaces come into contact, resisting their motion. The smoother the contact surfaces, the less friction there is, which allows them to move faster relative to one another.

When considering vehicle design, friction plays a key role. The speed at which a vehicle travels and the type of terrain it covers greatly influence the kind of wheels it needs.

Why Do Trains Use Metal Wheels?

Trains are designed to travel at high speeds over long distances while carrying enormous loads. They run on smooth, even tracks, allowing them to maintain speed with minimal friction. Metal wheels reduce friction significantly—by as much as 85% to 99%—compared to other materials. This is because both the rails and the wheels are made of smooth metal, allowing for a more efficient, frictionless motion.

Moreover, trains don’t need to stop abruptly. With their immense weight and power, they rely on momentum to keep moving, meaning they don’t require wheels that generate a lot of friction. Rubber tires, which would create much more friction, would require significantly more energy to move the heavy train, making them impractical.

Why Do Cars Use Rubber Tires?

Cars, on the other hand, need to travel on roads and often deal with uneven, unpredictable terrains, such as potholes and dirt roads. To handle this, cars need wheels that provide a strong grip, which is made possible by rubber tires. The friction between rubber and the road gives the vehicle the traction it needs to drive safely and smoothly.

Unlike trains, cars need to stop and start frequently. Rubber tires help facilitate quick stops and starts, providing the necessary friction for safe driving. Additionally, rubber tires are less expensive and easier to replace than metal wheels, making them a more practical choice for vehicles that experience regular wear and tear.

Conclusion: Friction Defines Wheel Design

In conclusion, friction is the most important factor influencing the design of wheels for different types of vehicles. Trains, which need to move rapidly with heavy loads, use metal wheels to reduce friction. Cars, which must navigate varied terrains, require rubber tires to increase friction and improve traction.