Safe Braking Distances Flashcards
6 cards from real LGV practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Safe Braking Distances flashcards as text
What is 'wheel lock-up' and how does ABS prevent it?
Answer: Wheel lock-up is when a braked wheel stops rotating but the vehicle continues moving — ABS modulates brake pressure to prevent this
Wheel lock-up occurs when brake force exceeds the tyre's grip, causing the wheel to stop rotating while the vehicle slides. A locked wheel has less stopping force than a rolling wheel at the threshold of grip. ABS prevents lock-up by rapidly releasing and reapplying brake pressure.
How does road camber affect an LGV's braking distance?
Answer: Adverse camber (leaning away from the bend) can reduce cornering grip and extend effective braking distance
Road camber affects the load distribution on tyres. Adverse camber (leaning away from a bend) shifts weight onto the outer tyres and reduces overall grip. When combined with braking, this can increase stopping distance and cause instability.
At highway speeds, how does cargo weight distribution affect emergency braking?
Answer: Rear-heavy loads reduce front axle weight, reducing front brake effectiveness and potentially causing the front to lock
Front brakes provide most of the stopping force. A rear-heavy load transfers weight to the rear, reducing the weight (and therefore grip) on the front axle. This reduces front braking effectiveness and can cause the front to lock or the vehicle to become unstable under emergency braking.
What is meant by 'tailgating' and why is it particularly dangerous for LGV drivers?
Answer: Following too closely — dangerous for LGVs because their stopping distances are far greater than cars, making a rear-end collision likely
Tailgating means following another vehicle with insufficient separation. For LGVs, their stopping distances are several times those of cars. Tailgating is dangerous because there is insufficient distance to stop if the vehicle ahead brakes suddenly.
What is the legal requirement for minimum tread depth on a goods vehicle rear axle tyre?
Answer: 1 mm across the central three-quarters of the tread width
For goods vehicles (LGVs over 3.5 tonnes), the minimum legal tread depth is 1 mm across the central three-quarters of the tread breadth, measured at any cross-section around the full circumference of the tyre. This is lower than the 1.6 mm requirement for cars.
Why must an LGV driver reduce speed before entering a bend, rather than braking in the bend?
Answer: Braking in a bend diverts grip from cornering to braking — this can cause loss of traction and instability, especially in a loaded vehicle
Tyre grip is shared between cornering force and braking force. If maximum grip is already being used for cornering, applying the brakes can exceed total grip capacity, causing a skid or rollover. LGVs with high centres of gravity are especially vulnerable. Slow before the bend, not during it.