Adherence, Tires and Brakes
Adherence, Tires and Brakes
The active safety of the vehicle depends fundamentally on its capacity to grip the asphalt and stop in time. In this article, we break down everything you need to know about brakes and tires to pass your theory exam.
1. The Braking System
The brake is the device responsible for reducing speed, stopping the vehicle, or keeping it stationary. It is vital to know the three types of braking devices that equip vehicles.
Brake Types
| Brake Type | Function | Action |
|---|---|---|
| Service Brake | Reduces speed and stops the vehicle safely. | Acts on all wheels. Operated by foot. |
| Parking Brake (Handbrake) | Keeps the vehicle immobilized (parked). | Generally acts on the rear wheels. |
| Emergency Brake | Emergency system that acts only if the service brake fails. | Must act on one wheel on each side of the same axle. |
Brake Classes: Disc and Drum
There are two main technologies. Today, most cars carry discs on the front axle (or on all 4 wheels), as they are more efficient.
- Disc Brakes: Pads press against a disc that turns integrally with the wheel. They have better ventilation and allow more progressive braking.
- Drum Brakes: Shoes expand inside a drum. They have worse cooling and higher risk of locking.
Correct Use and ABS System
To brake effectively and safely:
- Normal braking: Lift foot from accelerator (engine brake) and press brake pedal smoothly and progressively.
- Emergency braking: Must press fully, but trying not to lock wheels (if no ABS).
Important for the exam: The ABS (Anti-lock Braking System) prevents wheels from locking during sudden braking. Its main advantage is that it allows maintaining steering control while braking fully, being able to dodge obstacles.
Common Brake Failures
- Fading Effect: Excessive heating of brakes due to abusive use (e.g., going down a pass). Brakes lose efficiency. Solution: Use lower gears (engine brake).
- Spongy Pedal: May indicate air in circuit or brake fluid in bad condition.
- Wet Brakes: Lose efficiency. Dry them by tapping the pedal gently.
2. Wheels and Tires
Wheels are the only point of contact between the vehicle and the ground. They are composed of the metal part (rim) and the rubber part (tire).
Types and Maintenance
The use of tubeless tires is recommended, as in case of puncture, air is lost more slowly, reducing blowout risk.
Basic maintenance includes monitoring tread depth and inflation pressure.
- Tread Depth: Must be at least 1.6 mm in the main grooves of the tread. If less, replacement is mandatory.
- Expiration: Recommended to replace every 5 years, even if they have tread, as rubber hardens (crystallizes) and loses grip.
Inflation Pressure
Pressure must be checked periodically (once or twice a month) and always with cold tires.
| Pressure State | Consequences | Tire Wear |
|---|---|---|
| Correct Pressure | Maximum adherence and optimal braking. | Uniform wear. |
| Low Pressure (Little air) | Higher consumption, blowout risk, and heating. | Wear on sides (shoulders). |
| High Pressure (Too much air) | Lower adherence and bounces in suspension. | Wear in the center. |
3. Adherence and Skidding
Adherence is the force allowing the tire to grip the asphalt. If this force is lost, skidding occurs.
Causes of Skidding
- Driver: Excess speed, abrupt use of steering wheel or brakes.
- Vehicle: Worn tires or shock absorbers in bad condition.
- Road: Wet road, gravel, ice, or oil.
Aquaplaning
It is a dangerous phenomenon occurring when the tire cannot evacuate water on the road. A layer of water is created between wheel and ground, and the vehicle "floats", losing control and steering.
- How to avoid: Moderate speed and maintain tires with correct pressure and depth.
What to do when skidding
If the car skids, do NOT brake abruptly or declutch fully suddenly.
- Oversteer (goes from behind): Turn steering wheel towards the same side rear wheels skid (counter-steer).
- Understeer (goes from front): Stop accelerating and straighten steering slightly so wheels regain grip.
4. Wheel Change
In case of puncture, you must know how to act safely.
- Immobilize vehicle in safe, flat place. Apply handbrake and signal (triangles/V-16 light).
- Loosen nuts (without removing) before lifting car.
- Place jack and lift vehicle until wheel separates from ground.
- Remove screws and replace wheel.
- Tighten screws slightly, lower vehicle, and perform final strong tightening with car on ground.
Spare Wheel:
- Full Wheel: Has same characteristics as others. Can circulate normally.
- Temporary Use Wheel ("Biscuit"): Only serves to go to workshop. Has speed limitations (max 80 km/h usually) and distance.