Heavy Vehicle Pre-Trip Inspection: Tyres, Brakes, Lights, and Mirrors

For professional drivers operating commercial goods vehicles under C1, C, C1E, or CE licences, safety is not an afterthought—it is a legal and operational mandate. In Turkey, the Turkish Highway Traffic Regulation (Karayolları Trafik Yönetmeliği) places direct responsibility on the driver to ensure the vehicle is in roadworthy condition before starting any journey.

A thorough pre-trip inspection (yolculuk öncesi kontrol) is your first line of defence against mechanical failure, cargo damage, and road accidents. This lesson covers the essential maintenance and safety checks for the four most critical vehicle systems: tyres, brakes, lights, and mirrors.

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1. Tyre Condition and Pressure (Lastik Durumu ve Basıncı)

Tyres are the only contact point between your multi-ton vehicle and the road surface. For heavy goods vehicles (HGVs), tyre integrity directly governs braking distance, steering response, aquaplaning resistance, and fuel efficiency.

Tread Depth (Diş Derinliği)

The tread pattern on a tyre is designed to channel water away from the contact patch, preventing aquaplaning on wet roads.

• Legal Minimum: Under Turkish traffic laws, the absolute minimum legal tread depth for vehicle tyres is 1.6 mm.
• Heavy Vehicle Recommendations: For heavy goods vehicles, running on the absolute legal limit is highly risky, especially when carrying maximum cargo weights. It is recommended to replace tyres well before they reach 1.6 mm.
• Winter Regulations: In Turkey, commercial vehicles carrying passengers or goods are legally required to use winter tyres (kış lastiği) between December 1 and April 1 of each year. For these winter tyres, a minimum tread depth of 4.0 mm is highly recommended (and legally monitored in many commercial inspection checkpoints) to maintain traction on snow, ice, and slush.

Inflation Pressure (Lastik Hava Basıncı)

Tyres must be inflated strictly according to the manufacturer's specifications, which vary depending on the vehicle's axle load.

• Underinflation: Operating a vehicle with underinflated tyres increases rolling resistance, which elevates fuel consumption and causes rapid heat build-up. This heat can degrade the rubber compounds, leading to catastrophic tyre blowouts on the highway. Underinflation also causes the tyre sidewalls to flex excessively, compromising stability during cornering.
• Overinflation: Overinflating tyres reduces the contact patch with the road, leading to rapid, uneven wear in the centre of the tread and significantly reducing grip. It also makes the vehicle ride harsher, increasing wear on the suspension system.

Visual and Physical Inspections

During your pre-trip walkaround, inspect all tyres (including steering, drive, trailer, and spare axles) using a systematic approach:

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2. Braking System Inspection (Fren Sistemi Kontrolü)

Heavy goods vehicles rely on robust braking systems—typically dual-circuit pneumatic (air) brakes (çift devreli havalı frenler)—to decelerate loads that can exceed 40 tonnes. A minor defect in this system can translate into catastrophically long stopping distances or complete brake failure on steep declines.

Air Pressure Verification

Before moving a vehicle equipped with air brakes, you must ensure the system can build and maintain the correct operating pressure.

• Pressure Gauges: Ensure both primary and secondary air pressure gauges on the dashboard function correctly.
• Low-Pressure Warning: The low-pressure warning light and buzzer must activate if the system pressure drops below approximately 6 bar (90 psi). Do not drive if this warning is active.
• Pressure Build-Up Rate: With the engine running at fast idle, the pressure should build from 5 to 8 bar within the manufacturer-specified time limit (typically under 3 minutes).
• Leakage Rate Test: Shut off the engine, fully apply the service brake, and hold it for one minute. The air pressure drop must not exceed the legal limits (typically 3 psi or 0.2 bar per minute for single vehicles; 4 psi or 0.3 bar for combination vehicles).

Visual Component Checks

In addition to monitoring pressure gauges, perform a manual and visual check of the brake hardware components:

• Brake Pads and Shoes (Fren Balataları): Visually inspect the thickness of the brake lining material through the inspection ports. Pads or shoes worn past their wear indicators must be replaced immediately. Worn linings lead to metal-on-metal contact, ruining brake discs/drums and severely reducing stopping power.
• Brake Discs and Drums (Fren Diskleri ve Kampanaları): Check for heat cracks, deep scoring, or signs of extreme heat (blue discolouration). Severe cracking can lead to structural failure under heavy braking.
• Hydraulic and Pneumatic Lines: Inspect all flexible air hoses and brake lines for chafing, kinks, weathering, or leaks. Ensure hoses do not rub against moving suspension components or the road.

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3. Lighting Systems and Signaling (Aydınlatma ve Sinyalizasyon)

Proper illumination and signalling are vital for communication on the road. Due to their large dimensions and slower speeds, goods vehicles must be highly visible to other road users under all driving conditions.

Headlights: Dipped vs. Main Beams (Kısa ve Uzun Farlar)

Headlight alignment and cleanliness are critical for safe night driving and poor weather visibility.

• Dipped Beams (Low Beams / Kısa Farlar): Designed to illuminate the road ahead for at least 25 metres without dazzling oncoming drivers. Use dipped beams in urban areas, during twilight, and whenever visibility is reduced.
• Main Beams (High Beams / Uzun Farlar): Designed to illuminate the road ahead for at least 100 metres. Main beams must only be used on dark, unlit rural highways when there is no oncoming traffic or vehicles directly ahead. Switch back to dipped beams immediately to prevent temporary blindness (göz kamaşması) for other drivers.

Signaling and Warning Systems

Your intentions to turn, merge, or stop must be communicated clearly and instantly.

• Turn Indicators (Sinyal Lambaları): Under standard regulations, indicators must flash at a consistent rate of 60 to 120 flashes per minute. Check that all amber indicator lights are clean and functioning on both the tractor unit and trailer.
• Hazard Warning Lights (Dörtlü Flaşörler): Activating the hazard lights flashes all indicator lights simultaneously. These must only be used when the vehicle is stationary due to an emergency, breakdown, or when presenting a sudden, unavoidable hazard to other road users.
• Brake Lights (Fren Lambaları): These bright red rear lights must illuminate instantly when the brake pedal is depressed. Faulty brake lights are a primary cause of rear-end collisions by heavy vehicles.

Auxiliary and Specialised Lighting

• Fog Lights (Sis Farları): These project a low, wide beam designed to light up the road surface directly in front of the vehicle without reflecting off fog back into the driver’s eyes. Under Turkish regulations, fog lights must only be used during dense fog, heavy rain, or severe snowstorms. Using them in clear weather is illegal and subjects oncoming drivers to severe glare.
• Clearance and Side Marker Lights (Mani Lambaları ve Yan İşaret Lambaları): Vehicles exceeding certain widths and lengths must have functional amber side markers and red/white clearance lights to outline the vehicle's true dimensions in the dark.

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4. Mirrors: Calibration and Blind Spot Elimination (Aynalar)

Heavy goods vehicles have massive blind spots (kör noktalar) on all four sides. Properly selected, clean, and adjusted mirrors are your primary tools for maintaining situational awareness and avoiding collisions during lane changes, turns, and reversing maneuvers.

Mirror Classes and Fields of View

Modern commercial vehicles are equipped with a complex array of specialised mirrors:

• Class II (Main Side Mirrors): Provide a standard view of the traffic lanes to the rear-left and rear-right of the vehicle.
• Class IV (Wide-Angle Mirrors): Offer a curved field of view to see vehicles traveling in adjacent lanes directly beside the truck cab.
• Class V (Close-Proximity/Kerb Mirrors): Positioned above the passenger door, pointing downward to help the driver see low-profile vehicles, cyclists, or pedestrians adjacent to the passenger cab step.
• Class VI (Front-View Mirrors): Mounted on the front of the cab, pointing downward to eliminate the blind spot directly in front of the truck's high grille—a critical safety feature when starting from a standstill in pedestrian-heavy areas.

Calibration and Cleaning

Before starting your engine, ensure all mirrors are correctly adjusted. Never attempt to adjust mirrors while the vehicle is in motion.

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5. Environmental, Load, and Operational Variations

Your checks must adapt to environmental changes, cargo variations, and the specific route you are driving.

Impact of Weather and Seasonality

• Rain and Wet Roads: Wet tarmac reduces tyre friction by half. If your tyre tread depth is near the 1.6 mm limit, the risk of aquaplaning rises exponentially at speeds above 60 km/h. Wet conditions also require functioning windshield wipers and washers to keep your mirrors and side glass clean.
• Winter Driving: Cold temperatures reduce tyre pressure. If you are driving into high-altitude areas in Turkey (such as Eastern Anatolia), verify your winter tyres are fitted and inspect your snow chains (kar zincirleri) to ensure they are secure and the correct size for your drive axle tyres.

Heavy Load Considerations

• Tyre Flexing: Carrying high-tonnage cargo increases tyre deflection. You must adjust tyre pressures upward to the manufacturer’s maximum "loaded" rating.
• Brake Thermal Loading: Heavily loaded vehicles generate immense heat during braking. Ensure your auxiliary braking systems, such as engine brakes or retarders (retarder/egzoz freni), are fully operational before entering steep, mountainous descents to prevent the service brakes from overheating and failing (fren şişmesi).

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6. Common Violations and Critical Risk Scenarios

Failing to conduct proper pre-trip checks leads directly to traffic violations, fines, and severe accidents. Below are common real-world failure points that professional drivers must actively avoid:

1. Driving with Underinflated Tyres: This causes the tyre carcass to overheat, leading to sidewall blowouts. It also increases fuel consumption by up to 5% and creates unpredictable trailer sway.
2. Ignoring Squealing or Squeaking Brakes: Minor squeaks may indicate glazed brake pads, while grinding noises indicate completely worn linings. Ignoring these signs can lead to mechanical seizure, vehicle fires, or brake failure.
3. Improper Mirror Alignment with Over-Width Loads: If your cargo exceeds the standard width of your trailer, standard mirror positions will block your rear view. You must install temporary mirror extensions to maintain visibility.
4. Using High Beams in Urban Areas: Using main beams in illuminated city zones or when facing oncoming traffic causes glare, which is a common cause of pedestrian accidents in urban areas.
5. Relying Solely on Automatic Light Sensors: Modern trucks often feature automatic light sensors. However, these sensors do not always activate headlights during daytime fog or heavy rain. You must manually override the controls to turn on your dipped beams and ensure your rear tail lights are active.

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Summary of Cause-and-Effect Relationships

The condition of your vehicle’s safety equipment directly determines how it handles on the road:

• Correct Tyre Pressure & Tread Depth $\rightarrow$ Optimal traction, shorter stopping distances, resistant to aquaplaning, improved fuel efficiency.
• Incorrect Tyre Pressure or Bald Tyres $\rightarrow$ High blowout risk, severe understeer/oversteer, longer wet-braking distances, high fuel costs.
• Fully Serviced Air Brakes $\rightarrow$ Immediate deceleration, balanced braking force across all axles, safe mountain driving.
• Leaking Air Lines or Worn Linings $\rightarrow$ Delayed brake application, vehicle pulling to one side, dangerous brake fade, risk of runaway vehicle.
• Clean, Aligned Lights $\rightarrow$ Clear communication of driver intentions, early detection of road hazards, zero glare for oncoming drivers.
• Obstructed, Broken, or Misaligned Mirrors $\rightarrow$ Massive blind spots, side-swipe collisions during lane changes, high risk of striking pedestrians/cyclists during tight turns.

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