lesson 9.2 TIRES AND TRACTION Tires are a key part of your control system. The way your tires interact with the surface of the road is essential to safe driving.

Explain how traction controls your car. OBJECTIVE

Friction and Traction Friction is the force that acts between materials as they move past each other. How can you feel the force of friction by rubbing your hands together?

When tires roll over the surface of the road, they create traction. Traction makes your vehicle grip the road so you can control speed and direction.

The traction of the tires on the roadway pushes your vehicle forward. Braking causes the friction of the brake linings against the brakes to slow the wheels. Traction between the tires and road will slow your vehicle. Traction also enables your vehicle to turn left or right when the front wheels turn.

Describe the importance of tread and proper inflation in maximizing traction. OBJECTIVE

Tire Tread and Traction The place where a tire touches the road is called its footprint. This picture shows the red patch under the tires that form the footprint. These small footprints are all you have for traction on the road surface.

The grooved surface of a tire is called tread. Tread provides the traction for starting, stopping, and gripping the road. Tread helps prevent skids and hydroplaning.

The amount of tread touching the road increases the gripping power of traction. Tire size also affects the amount of tread and traction on the road. Check the owner’s manual for your vehicle for the maximum recommended size of tire.

Inflation and Traction Properly inflated tires can mean the difference between keeping or losing control. Too much or too little pressure can change the amount of tread, or footprint, on the road. Properly inflated tires grip evenly.

This tire shows how a properly inflated tire will grip the road better than an underinflated or overinflated tire.

Underinflated tires as shown in this picture grip only by the outer edges.

This picture shows an overinflated tire that grips only in the center.

Underinflation When you drive on an underinflated tire, only the tire’s outer edges provide traction. Why is it dangerous to drive on an underinflated tire?

Overinflation Compare the footprints of these two tires. Which tire will wear out in the center faster?

Temperature Weather can change tire pressure. Cold air makes tire pressure drop, and tires can become underinflated. Hot temperatures will increase pressure, and may cause overinflation.

Check your tires’ pressure regularly. Should tires be checked when they are hot or cold? Before you start driving, or after driving for awhile?

Identify the driver actions that depend on traction and how they relate to vehicle control. OBJECTIVE

Using Traction Traction is used to accelerate, brake, and steer. Your tires provide a limited amount of traction. Hard braking can consume most of the traction. Combined hard braking and steering can cause a loss of control.

Imagine you enter this curve at 55 mph Imagine you enter this curve at 55 mph. As you reach the middle of the curve, you realize you are going too fast, so you quickly brake and turn the wheel sharply into the curve. What would probably happen?

How could you have managed your traction to remain in control?

Did You Know? Tire Pressure You can’t tell just by looking if your tires are properly inflated. A tire that is underinflated by 40% can look just like a properly inflated tire.

Identify three factors that can reduce traction. OBJECTIVE

Ensuring Good Traction Three things are required to achieve ideal levels of traction. vehicle condition road surface driver actions

Vehicle Condition Why is a new vehicle easy to control? Why are older vehicles more likely to have reduced control systems?

Tires are your lifeline to traction. What should you check regularly? If a tire is punctured, it could suffer a blowout, when all of the air escapes at once. When shock absorbers are worn, how will this affect your tires and traction?

Road Condition A dry, flat road with good tires gives you excellent traction. Describe some road conditions that can reduce traction.

What road conditions could cause you to lose steering, braking, or acceleration control? Will water freeze in shaded areas and on bridges before it does on regular roads?

What actions can you take when road conditions are about to change?

Driver Action Your actions affect your ability to manage traction. What driver actions can consume a lot of traction? What driver actions can maximize traction?

lesson 9.2 review What three actions consume traction? What steps can you take to ensure that an older car will have good traction?