# Tires

## It's All About Traction

### Tire Pressure

The amount of force, in pounds, exerted on the sidewalls of the tire per square inch – or PSI

The area of the tire that touches the ground, or the TIRE PATCH, creates a frictional force called TRACTION with the surface. Tires with too high or low of pressure do not have the optimal size tire patch which causes problems with surface traction.

• Rolling resistance
• damage: popped tube
• little comfort
• + rolling resistance
• + damage: pinch flat
• - responsiveness

Adjust tire pressure to accommodate for:

• Road or trail conditions
• Weather conditions
• Tire type
• Temperature
• Altitude

The pattern along your tires’ rubber changes the force of friction along the road or trail.

• A smooth pattern, like on a road bike, decreases resistance with pavement
• A knobby pattern, like on a mountain bike, helps keep traction with a trail

#### Tire Size

A tire with a smaller diameter accelerates faster, however a larger diameter tire will clear obstacles easier due to the IMPACT ANGLE.

## Bicycle Gyroscope

### Is the Wheel Defying the Laws of Physics?

Have you ever noticed that it seems difficult to balance your bike when moving at very slow speeds? When you pedal, you increase your speed and create angular momentum which helps you maintain a stable, upright position.

#### Slow Speed:

Low angular momentum

#### Faster Speed:

High angular momentum

A rotating bicycle wheel acts as a gyroscope. It is thought that the gyroscopic effect plays a major role instability and control when riding a bike. A gyroscope is based on the principle of angular momentum.

moment of inertia: describes an objects tendency to resist angular acceleration

Thus,

When a wheel is spun, it develops angular momentum which causes the wheel to resist changes in orientation as explained by the law of conservation of momentum. This states that the angular momentum must remain constant in both magnitude and direction unless acted on by an outside force.

angular momentum initial = angular momentum final

Although the gyroscope tries to maintain its orientation, outside forces such as friction act on the gyroscope causing it to eventually lose its angular momentum as the wheel’s speed decreases.