Emergency braking situations can happen when you least expect them – a child darting into the road, traffic suddenly stopping ahead of you, or an obstacle in your path that appears without warning. Your natural reaction may be to slam on the brakes.
But should you avoid fully locking them up? The answer is yes, you are generally better off not locking up your wheels in an emergency braking situation. Here’s a more in-depth look at why.
The Dangers of Locked Brakes
When you fully press the brake pedal, it activates your vehicle’s hydraulic braking system and clamps down the brake pads against the rotors to slow the wheels. If you press too hard, the braking force overwhelms the available traction between the tires and the road surface, causing the wheels to stop rotating while the vehicle keeps moving forward. This is known as a skid or a lock-up.
Locked wheels have some significant disadvantages when trying to slow your vehicle quickly:
- Loss of steering control – With the wheels frozen in place, you lose the ability to steer or maneuver the vehicle. This could prevent you from taking evasive action to avoid a collision.
- Longer stopping distances – Locked wheels actually increase stopping distances on dry pavement compared to threshold braking. The tires are not rolling and have less kinetic friction force working to slow you down.
- Reduced stability – Locked wheels can cause the vehicle to skid in an uncontrolled manner. This unpredictable movement makes it harder to maintain stability and control.
- Flat spots on tires – Skidding on locked tires generates a lot of heat and friction, which can cause flat spots and damage on the portion of the tire in contact with the pavement. This requires tire replacement sooner.
So in most everyday situations, you want to avoid fully locking up the brakes and try to keep the wheels rolling when braking hard. This provides the shortest stopping distance while also maintaining vehicle stability and control.
The Benefits of Anti-Lock Brakes
Modern vehicles are equipped with anti-lock braking systems (ABS) to help avoid wheel lock-up during hard braking. This advanced system uses sensors at each wheel to detect when they are slowing down and on the verge of a skid. It then rapidly pulses the brakes on and off up to 15 times per second to keep the tires rolling right at the point of lock-up.
ABS provides several advantages when you need to stop quickly:
- Prevents wheel lock – The pulsing action keeps the wheels from fully locking so you maintain steering control.
- Shortens stopping distance – By keeping the wheels rolling, ABS allows you to brake harder while maintaining optimal tire grip and friction to stop in the shortest distance possible.
- Maintains stability and control – Avoiding lock-up helps keep the vehicle stable and headed in the intended direction during abrupt braking on slippery surfaces.
- Allows for evasive steering – With the wheels still rotating, quick steering inputs can be made to help avoid hazards in an emergency situation.
- Reduces tire flat-spotting – The pulses prevent the tires from skidding in one spot for too long, minimizing damage to the tread.
So with ABS-equipped vehicles, you can press hard on the brake pedal without needing to ease off if the wheels start to lock. This allows you to brake to the maximum in an emergency while still benefiting from enhanced control and stability.
Emergency Braking Technique for Non-ABS Vehicles
For older vehicles without ABS, the emergency braking technique requires more skill and practice on the part of the driver. You have to manually modulate the brakes to balance maximum braking force versus maintaining steerability. This is known as threshold or cadence braking:
- Press the brake pedal firmly – You want high initial braking pressure, but not to the point of lock-up. Press down steadily on the pedal to engage maximum braking force right before the wheels lock.
- Feel for impending wheel lock – If the vehicle begins shuddering or vibrating and steering control becomes reduced, this signals the wheels are nearing lock-up.
- Ease off the brakes slightly – As soon as you sense lock-up, let off the brake pedal just a bit to let the wheels turn again. This will restore traction and steering.
- Reapply the brakes fully – Immediately after the wheels start rolling, press the pedal down firmly again to the threshold of lock-up.
- Repeat cadence as needed – Continue modulating the brakes to balance stopping power versus retained steering and stability.
It takes a delicate touch and quick reflexes to properly cadence brake a non-ABS vehicle. With practice, you can learn the feel of impending lock-up and release brake pressure accordingly. Race car drivers routinely train in emergency braking techniques to react effectively in high-risk situations.
Tips for Emergency Braking Situations
- Stay alert and scan ahead to identify risks early so you have more time to react. The sooner you begin braking, the more distance you have to stop.
- Press firmly on the brake pedal to get maximum power immediately – don’t be shy. For non-ABS vehicles, you can release pressure if the wheels lock but you need that initial force applied.
- Don’t pump the brakes if you have ABS – this will disable the system. Press down hard and let ABS handle the rapid pulsing for you.
- Look and steer where you want to go to maintain as much control over the vehicle as possible while braking hard.
- Downshift to use engine braking in conjunction with wheel brakes if it is safe to do so.
- Avoid overly abrupt steering inputs that could further upset vehicle stability when braking near the limits of traction.
- Steer around obstacles if possible when braking hard instead of locking up the wheels trying to stop in time.
- Check brake system regularly – properly functioning brakes are critical to emergency stopping capability so inspect pads, rotors, fluid levels and components often.
Avoiding wheel lock-up during emergency braking is ideal for maintaining control and stability of your vehicle. Anti-lock brakes are designed to allow hard braking without lock-up but require full pedal pressure. On non-ABS vehicles, threshold braking involves modulating pedal pressure to remain at the maximum braking force possible before lock-up. With practice, this technique can approximate the benefits of ABS. Stay alert, brake early and steer out of danger whenever possible. Proper emergency braking skills can help avoid accidents and safely handle those sudden crisis moments we all eventually face on the road.