When Should You Not Use Retarders? An In-Depth Guide for Drivers

As a professional driver, you know that retarders are essential tools for safely managing speed and reducing wear on your truck‘s brake system. But you also need to understand when NOT to activate these auxiliary brakes to avoid potential skids or loss of control. This comprehensive guide provides everything you need to optimize your use of retarders.

How Do Retarders Help Slow the Truck?

Retarders create drag force to slow wheels and vehicles. Here‘s a quick physics recap:

Force = Mass x Acceleration

The retarder applies a counterforce which:

• Slows wheel acceleration
• Creates negative torque at wheels
• Delivers higher negative acceleration
• Ultimately reduces vehicle kinetic energy

This force opposes motion using principles of friction, fluid dynamics, electromagnetism, etc. depending on the retarder design. But the effect is always the same – slowing the rig by controlling wheel speed.

Hydraulic retarder components (image credit: KWSTNET)

Why are Retarders So Important?

• Retarders provide 30-40% of a heavy truck‘s total braking power.
• They can reduce service brake use by 50% or more on steep descents.
• Retarders extend brake lining life by 3-4 times compared to relying solely on service brakes.
• Newer precise retarder controls allow the truck to remain in gear longer for optimal engine braking.
• Retarders give the driver greater flexibility in braking strategy.

With the ability to take over a significant share of braking duty, retarders are invaluable tools for combating brake overheating and reducing maintenance costs. But it‘s critical to use them judiciously.

Slippery Road Hazards

Activating the retarder on wet, snowy or icy roadways can lead to wheel lockup and dangerous loss of control. For example:

• A fully loaded logging truck descending a 6% grade at 60 mph encountered a patch of black ice. The driver applied the retarder which locked the drive wheels, causing a jackknife skid. The truck overturned, resulting in critical injuries.

• A concrete mixer lost traction on a bridge deck when the driver engaged the retarder. The abrupt wheel lockup caused the rear of the truck to swing out, sideswiping an oncoming car.

• Numerous retarder-related mishaps have occurred on snowy mountain passes and icy bridge decks. The "surprise" traction change overwhelms even high-quality ABS systems.

As surface friction decreases, so does the amount of braking force the wheels can transmit before sliding. The retarder isn‘t "smart" enough to automatically compensate for less grip. Only the driver can prevent retarder lockup by turning it off preemptively before hitting slippery surfaces.

More Retarder No-No‘s

Short/moderate grades – Let gravity and gentle service braking handle the speed instead of overworking your retarder.

Parking on slippery ground – The abrupt retarder stopping action can cause skids as the weight transfers forward.

Descents with changing traction – Constantly monitor and modulate retarder versus service brake use.

Approaching intersections or traffic queues – The retarder can‘t initiate an emergency stop if needed, so switch it off in time.

Malfunction or abnormal operation – Have the retarder inspected if it‘s not slowing effectively or the controls are unresponsive.

Failed/overheated service brakes – Get the brakes repaired immediately. The retarder alone won‘t stop the vehicle.

When in doubt, turn it off – Service brakes are the sure stopping solution. Don‘t gamble with the retarder.

Retarders and Noise Pollution

Retarders have one notorious side effect – loud noise as they slow the drivetrain using engine compression. Their repetitive braking action produces a characteristic loud "machine gun" sound.

This has led some jurisdictions to impose nighttime bans on retarder use in residential neighborhoods or noise-sensitive areas. For example, Aspen, Colorado prohibits retarder use within city limits except in cases of emergency.

While critical for safety, it‘s prudent for drivers to minimize retarder noise impacts by:

• Reducing repetitive on/off cycles – use lower levels for steady deceleration.
• Accelerating smoothly through gear shifts to avoid RPM spikes.
• Choosing alternate routes circumventing neighborhoods when possible.
• Reporting any faulty muffler/exhaust noises which amplify braking sounds.

Maximizing Control on Downgrades

Proper coordination between the retarder and service brakes provides the best downhill speed control while minimizing system heat. Here are some tips:

• Activate the retarder once speed has stabilized after cresting the hill.
• Apply intermittent, gentle service braking if the retarder alone isn‘t sufficient.
• Use a touch-and-release braking cadence for optimal heat dissipation.
• Downshift judiciously at low RPMs – excessive engine braking can overspeed components.
• Avoid riding the retarder excessively – cycle between retarder and brake applications.
• Monitor brake temps and let them cool after long descents.

Brake temperature profiles – continuous vs. cyclic braking (Image credit: Chris Mi, University of Ontario Institute of Technology)

The optimal balance depends on the grade, road speeds, vehicle weight and the driver‘s comfort level. Don‘t be afraid to utilize your service brakes regularly – that‘s what they‘re designed for!

Reading the Road Surface

Your primary defense against retarder-related skids is reading the road‘s traction. Watch for these cues:

• Shaded areas, bridges and overpasses with potential ice buildup.
• Snow or slush – even a thin layer can be slippery.
• Rain, water puddles or wet leaves reduce traction.
• Gravel, dirt and mud can coat the road intermittently.
• Warning signs for slippery conditions ahead.

If you sense reduced grip for any reason, proactively turn off the retarder and prepare to stop using just the service brakes. Their individual wheel control will help maintain stability.

The Weight Shift Braking Hazard

Under braking, weight transfers forward reducing the rear axle normal force and its tire grip:

The front tires account for a greater percentage of total braking on a downgrade, especially with the retarder. If they start to lock and slide, stability is severely compromised. This is another reason to disable the retarder on slippery surfaces.

Common Retarder Q&A

Q: Won‘t my ABS system compensate automatically if the tires lock during retarder braking?

A: No, ABS only modulates the service brakes not the retarder. It also can‘t recover from a full lockup once it occurs.

Q: But the service brakes alone heat up rapidly on steep hills, don‘t they?

A: Yes, that‘s why you alternate between retarder and friction braking to allow cooling periods. The split reduces overheating.

Q: What is the maximum descent grade most retarders can handle alone?

A: Around 6-7% for fully loaded trucks. Beyond that, some service braking is needed to avoid overspeed.

Well-Engineered Retarders

Some truck makers are renowned for the power and sophistication of their integrated retarder systems:

• Volvo Trucks – Offers high capacity two-stage turbo compounding with the VEB+ engine brake.

• PACCAR – Uses a variable geometry turbocharger to increase engine braking across RPMs.

• Daimler Trucks – The Detroit Assurance suite optimizes engine brake and exhaust brake staging.

• Scania Trucks – Retarder capacity tailored to individual powertrain configurations using 3D simulations.

Look for advanced features like multi-mode operation, variable vanes, and automatic temperature-based derating to maximize retarder effectiveness while protecting driveline components.

By fully utilizing your truckʼs braking system while understanding the limits of retarders, youʼll handle any mountain downgrade safely. But stay focused and ready to react in case the road conditions turn against you. Your skill as a driver is ultimately what keeps the shiny side up! Let me know if you have any other retarder-related questions.