The car – construction and systems

The car's main systems

You do not need to be a mechanic to get a driving licence, but you must understand the car well enough to use it safely and discover faults before they become dangerous. A modern car is made up of several systems that work together. When you know the role of each system, you also understand why warning lights, strange noises or changed behaviour should be taken seriously.

The most important systems

• Engine and power transmission: provide movement and transfer power to the wheels.
• Brakes: reduce speed and keep the car stationary. The most important safety system you have.
• Steering: lets you change direction precisely and predictably.
• Wheels and tyres: the car's only contact with the road – all speed, steering and braking go through them.
• Lights and visibility: make sure you see and are seen.
• Safety equipment: seat belts, airbags, head restraints and the body's deformation zones.

The engine produces power, but that power must be controlled before it reaches the wheels. A clutch or automatic transmission connects the engine gradually, the gearbox selects the ratio, and the drivetrain sends power to the driving wheels. A low gear gives strong pulling force at low speed, while a high gear gives calmer engine running once the car is moving.

Why understand the car?

As the driver, you are responsible for the car being in roadworthy condition every time you drive. If you know the systems, you understand what a warning light means, why the braking distance increases on a slippery road surface, and when you should stop and get help instead of driving on.

The colour, not the symbol, tells you how urgent it is: red means stop, yellow means get it checked soon.

Active safety: Features and equipment that help the driver avoid an accident, for example good brakes, good road grip and good visibility.

Brakes, steering and driver assistance

The brakes are the car's most important safety system. They convert movement into heat and reduce speed. A normal braking system is divided into two circuits, so that you retain some braking effect even if one circuit should fail.

The foot brake works hydraulically: pedal force becomes pressure in the brake fluid, and the pressure pushes pads or shoes against discs or drums at the wheels. Friction turns movement energy into heat. That is why brakes can lose effect if they become too hot, or if fluid/air in the system does not transfer the pressure correctly.

The circuits are split diagonally. If one fails you still brake on two wheels – but the pedal goes further and so do you.

Service brake and parking brake

• You use the service brake (foot brake) while driving to reduce speed and stop.
• The parking brake (handbrake or electric) keeps the car stationary when it is parked.
• Engine braking occurs when you release the accelerator while in gear; it relieves the foot brake on long downhill gradients.

ABS and electronic assistance systems

Modern cars have several systems that help you retain control, but they do not cancel the laws of physics. They give you a little more margin – they do not remove the need for adapted speed and a good distance.

ESC brakes a single wheel and twists the car back on course. It cannot create grip that is not there.

A locked wheel slides where the car already points. Keep the pedal down – with ABS the wheel rolls enough for you to steer around.

Steering

Power steering makes the steering wheel easy to use. If you notice that the steering suddenly becomes heavy, that the car pulls to one side, or that the steering wheel vibrates, it may be a sign of a fault – for example low tyre pressure, a fault in the power steering or uneven tyre wear. You should then investigate the cause before driving further.

Steering is also affected by load, tyres and speed. Heavy load far back or on the roof can make the car slower to turn and more unstable in an evasive manoeuvre. Incorrect wheel alignment or unequal tyre pressure can cause uneven wear and make the car wander or pull to one side.

Simple tests you can do yourself

Understeer and oversteer

When grip fails, it rarely fails equally at the front and the rear. Which end lets go first decides what the car does - and both nearly always start with too much speed into the bend.

Cruise control and adaptive cruise control

Cruise control holds a set speed without you keeping your foot on the accelerator. Adaptive cruise control uses radar or a camera and also keeps the distance to the car ahead by accelerating and braking on its own. Both are comfort systems. They do not watch the road for you, and they do not move responsibility for your speed away from the driver.

• Ordinary cruise control holds the speed even when the car ahead slows down – there you have to brake yourself.
• The system disengages when you brake, and on most cars also when you press the clutch.
• Adaptive cruise control is poor at seeing a vehicle that is already stationary, and can react late to a queue that has come to a complete stop.
• On a long downhill the system cannot always hold the speed down on engine braking alone, and the speed creeps over the limit.

ABS: Anti-lock brakes. Prevents the wheels from locking during hard braking, so that the driver can steer and brake at the same time.

Tyres and road grip

The tyres are the car's only contact with the road. The total contact patch with the surface is no bigger than a few palms. All acceleration, steering and braking must happen through these small patches. The condition of the tyres is therefore absolutely crucial for safety.

Four patches the size of your palms carry everything you ask the car to do.

Tread depth

The tread channels away water, snow and slush so that the rubber makes contact with the road surface. Worn tyres give poorer grip and a much longer braking distance, especially on wet and slippery roads.

The tread must push the water away in time. If it is too shallow, or the speed too high, the tyre rides up on the water.

Air pressure

• Too low pressure gives higher fuel consumption, poorer steering and a risk that the tyre will overheat.
• Incorrect pressure gives uneven wear and a shorter service life.
• Check the pressure when cold, and use the values specified by the car manufacturer (often on a label in the door frame or in the fuel filler flap).

The wrong pressure moves the contact patch: too low wears the shoulders, too high wears the centre – and grip suffers either way.

Summer tyres and winter tyres

Winter tyres have a softer rubber compound and a tread pattern that gives grip on snow and ice. Studded tyres provide extra grip on ice, but cause more wear to the road and may be used only during a specified winter period. Non-studded winter tyres can be used all year, but are not made for summer heat. Whatever the tyre type, you as the driver are responsible for the car having tyres that suit the road conditions.

Markings you should recognise

• The Alpine symbol - a mountain with a snowflake inside - shows the tyre has been tested and approved for winter conditions. The letters M+S alone are not the same; they are only a manufacturer's claim with no test requirement.
• Tread wear indicators are small rubber bars down in the tread grooves. When the tread has worn level with them, the tyre is at the legal minimum for summer tyres and must be replaced.
• The production date is four digits in an oval on the sidewall: week and year. Rubber ages and hardens even when the tyre still has plenty of tread depth.

Spare wheel and punctures

Tread depth: The depth of the grooves in the tyre. Channels away water and snow so that the tyre gets grip. At least 1.6 mm in summer and 3.0 mm from 1 November to the first Sunday after Easter Monday.

Lights, visibility and the distinctive features of electric cars

Seeing and being seen is a prerequisite for safe driving. The car has several groups of lights, each with its own task, and you must know when to use which.

Light groups

Dipped beam stops well short of the pedestrian. On dipped headlights your speed must match how far the light reaches.

Visibility

• Clean windows, mirrors and lights are part of the daily check – dirt and ice steal visibility.
• Working windscreen wipers and washer fluid that tolerates cold are necessary all winter.
• Make sure you have clear visibility before driving; scrape all ice and remove snow from the roof and lights.

Electric car and hybrid

More and more people drive electric cars. They have some distinctive features you should know, but the same traffic rules apply fully.

• The electric car is almost silent at low speed – vulnerable road users do not hear you coming, so be extra attentive near pedestrians and cyclists.
• Powerful and instantaneous acceleration means that speed increases quickly; it requires a conscious accelerator foot.
• Regenerative braking (engine braking) charges the battery when you release the accelerator, and reduces wear on the ordinary brakes.
• Range falls in cold weather and at high speed – plan charging on longer journeys.

Lift off and the motor becomes a generator, slowing the car. The foot brake must still always be ready.

Electric cars are often heavy because of the battery. High weight can feel stable, but it increases the energy that must be stopped in an emergency braking and can increase tyre wear. Combined with quick acceleration, steady speed, good distance and correct tyre pressure become especially important.

The safety equipment built into the car

The bodyshell is not just a skin. The front and rear are designed to deform in a controlled way in a crash, so the forces build up over time rather than hitting your body in an instant. The passenger cell around you, by contrast, is designed to keep its shape. The sides are the weakest direction, because there is so little space between you and whatever you hit - which is why side airbags and reinforced pillars matter so much.

Belt and airbag work together

• The three-point belt spreads the forces over hip, chest and shoulder. That is far better than a lap belt alone, which only holds you back at the waist.
• The belt tensioner pulls the belt tight against your body the moment the crash begins, so you do not build up speed before the belt catches you.
• Thick outer clothing puts several centimetres of slack into the belt. Take off the padded jacket before you buckle up.
• The airbag inflates in about a hundredth of a second and only fires in an impact of a certain force - low speeds do not set it off.
• Sit at least about 25 cm from the steering wheel. Closer than that and the bag can hit you while it is still inflating.
• An airbag without a belt is dangerous: without the belt you meet the bag before it has finished deploying.

Whiplash: An injury caused when the head is thrown backwards and then forwards, most often in a rear-end collision. A correctly adjusted head restraint - top edge level with the top of the head and as close to the back of the head as possible - is what limits the movement.

Regenerative braking: The electric car's ability to brake by letting the electric motor act as a generator and charge the battery, instead of only using the ordinary brakes.