Chapter 13: Traction, Tires and Brakes

1. Adhesion

The grip of the tyre with the road. The best adhesion occurs on a rough and dry road surface. In rain and/or ice, adhesion is reduced.

2. Tyres/tires

Parts of a tyre

1. Pneumatic part: formed by the cover, air and tube (if it has one).

2. Metallic part: rim

Types of tyres:

With tube: rarely used	Without tube (tubeless): better because they reduce the risk of blowout
Compressed air is retained inside the inner tube.	Airtight coating that replaces the inner tube

Replacement tyres must have the approved dimensions and characteristics, or authorised equivalents. Tyres on the same axle must be of the same type; follow the vehicle manufacturer’s specifications, including load and speed ratings.

It is RECOMMENDED to replace worn tyres before reaching the legal limit. The MANDATORY minimum depth in the main grooves is 1.6 millimetres for cars, light vans and trailers up to 3,500kg; it is 1.0 millimetre for buses, heavy goods vehicles and heavier trailers. There is no general compulsory replacement every 5 years: inspect ageing tyres and follow the manufacturer’s advice.

The picture shows an approximate coin check; use the wear indicators or a tread-depth gauge for a reliable measurement.

Wider tyres may increase fuel consumption; grip also depends on tyre design, pressure and road conditions, so width alone does not guarantee better adhesion.

Tyre pressure should be checked with cold tyres and the manufacturer’s recommended pressure for either winter or summer must be followed.

Use the approved tyre speed rating. Special tyres have specific authorised exceptions; if their rating is below that on the vehicle’s technical card, their speed limit must be displayed where the driver can see it. For winter-restriction compliance with tyres, vehicles up to 3,500kg MMA need 3PMSF-certified tyres on every axle; M+S alone is insufficient.

Inflate the spare wheel to its specified pressure, which may differ from the other tyres. When driving with a temporary spare wheel, it is required to:

• Observe the maximum speed marked on the wheel or in its instructions, commonly 80km/h
• Observe the manufacturer’s distance and use limits; there is no universal 200km allowance
• Its purpose is to help the vehicle reach the nearest workshop to repair the tyre or replace it with a new one

Less air in the tyre (underinflated)	More air in the tyre (overinflated)
Wears down on the sides Decreases adhesion and consumes more fuel	Wears down more in the center Can damage the suspension

If a wheel is unbalanced (due to blows or bumps), go to the workshop.

In case of a puncture, despite changing the wheel, you should go to the nearest workshop.

In case of a tyre blowout, hold the steering wheel firmly, ease off the accelerator and avoid sudden braking or steering. Once the vehicle is stable, brake gently and stop in a safe place.

3. Brakes

Brake defects can make a vehicle unsafe and cause it to fail its ITV inspection; regular maintenance is essential.

Braking systems:

• Service brake: located on a pedal, it is operated with the foot and brakes all wheels
• Parking brake: the hand brake, used for parking, normally brakes the rear wheels
• Emergency brake: the secondary braking function allows the vehicle to be stopped if the service brake fails; it is not necessarily automatic and is different from AEB collision braking

Types of brakes:

• Disc: uses friction pads
• Drum: uses friction shoes

Disc brakes are better, since they cool and dry better when uncovered.

Maintenance: Check the brake fluid and replace it when indicated by the manufacturer. It can heat up and absorb moisture over time; a falling level or leak requires inspection, not simply topping up.

If the brake pedal feels light or spongy, there may be air or another fault in the hydraulic system. Have it checked promptly.

If the pedal travels almost to the floor or braking is weak, stop safely and arrange assistance; low fluid, a leak or another brake fault may be responsible.

The brake servo reduces the pedal effort needed. On long descents, use a suitable low gear and engine braking to avoid overheating the brakes; never coast in neutral.

ABS helps prevent wheel locking and preserves steering control during hard braking, but cannot guarantee grip or a shorter stopping distance on every surface. In emergency braking with ABS, press the brake firmly and continuously; do not pump it, even if the pedal vibrates.

In case of skidding:

• Skidding front axle: ease off the accelerator and reduce excessive steering smoothly until the front tyres regain grip; do not turn more sharply or brake abruptly.
• Skidding rear axle: look where you want to go and steer gently towards the side to which the rear is sliding; straighten smoothly as grip returns and avoid abrupt braking.

3.1 Braking effectiveness

Depends on:

• The condition of the brakes and brake fluid
• The pressure applied to the brake pedal
• The tyres
• The state of the road, speed and mass of the vehicle

3.2 Tyre wear

Can be increased by:

• Driving style
• Vehicle speed
• The weather (+ wear in summer)
• Load and mass
• Incorrect tyre pressure