Exploring Hill Descent Control for 4WDs

One common addition to most 4WDs is Downhill Assist or Downhill Descent Control.

Michael Ellem
Oct 26 2023

We've discussed technology in 4WDs at length. Today's 4WDs incorporate various tech features to aid novice 4WD drivers in navigating tracks. One common addition to most 4WDs is Downhill Assist or Downhill Descent Control.

Downhill descent control offers a straightforward approach to managing your vehicle's speed when navigating steep terrain. It's a manual system, allowing you to activate and control it as needed. While it's optional, for many, this feature proves invaluable for maintaining better vehicle control, particularly on steep and rugged terrain.

As the name suggests, it serves as an aid for regulating descent speed. But how does it operate? It leverages the ABS systems found in modern vehicles to control the speed, primarily by using the braking system. Yes, it's the braking system that plays a key role in slowing down the descent. You can hear this in action as the brakes intermittently engage and release, with the callipers applying pressure to the brake pads against the disc rotors.

There are several potential challenges that can arise when driving any 4WD in steep terrains, for example, the Victorian High Country.

When descending steep hills, the instinct might be to apply significant pressure to the brakes to slow down the descent. Many individuals choose to keep their vehicle in drive while descending steep slopes and rely heavily on braking to control their speed. Even when in low range, if the vehicle remains in drive, it will continue downhill unless brake pressure is applied. The concern here lies in the possibility of excessively heating the brakes during an extended descent down a hill. This excess heat is then transmitted through the disc rotors and into the hubs and bearings of your drivetrain.

Now, what happens when you reach the base of a hill in the High Country? Typically, you'll encounter a water obstacle, such as a creek or river crossing. Herein lies the issue: if you attempt to traverse the water crossing with hot brakes and wheel bearings, the water will rapidly cool and quench the metal components and differential housings. This sudden cooling can lead to the ingress of water through seals. When water mixes with grease or oils, it has the potential to result in mechanical component failures at some point during your journey.

To prevent such failures, you can take a straightforward, preventative approach. Use low range and manually select lower gears, enabling the engine to act as a brake and decelerate your descent. This method minimizes the need to apply the brakes. By the time you reach the base of the hill, you'll be able to confidently navigate the river crossing, assured that your drivetrain isn't excessively heated. You can then proceed up the opposite side of the hill without concerns.

Here's a quick tip: When navigating steep terrain with loose, rutted surfaces, it's common for the vehicle's weight to be concentrated over the front axles. As a result, the rear tires may experience a loss of traction as they traverse through ruts. One of the rear tires will firmly grip the loose terrain while the other, moving through the rut, will have less pressure and, consequently, less traction, causing the vehicle to move forward rapidly.

If your vehicle is equipped with a rear differential lock, engage it while descending through rutted terrain. This action binds the two rear tires together, preventing the loss of traction and ensuring a safer descent through rough, rutted terrain.

Utilising engine braking and low range gears is one of the most important controls when 4WDing to ensure that slow rates of descent are achieved, providing safe travels in steep terrain.

Leveraging engine braking and low range gears represents one of the most crucial techniques in 4WDing. It ensures that you maintain controlled, gradual descents, enhancing safety when navigating steep terrain.

While automated hill descent control systems offer valuable assistance to novice 4WD drivers, it's essential to be mindful of the stress that prolonged hill descents can place on your vehicle. Long descents can result in elevated heat within the braking systems, hubs, and bearings, mainly due to the intermittent use of brakes.

However, it's important to highlight that modern 4WDs come equipped with a range of tools to address these challenges. In addition to hill descent control, you have the advantage of low range and engine braking at your disposal. These features collectively ensure a safer and more comfortable journey, particularly when you encounter extended downhill stretches in areas like the High Country.


-Michael Ellem | Offroad Images

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Michael Ellem
Michael Ellem is a long term friend of the Club 4X4 Insurance and voice of The Campfire. He is also an expert adventure, 4X4 photographer from the renowned Offroad Images and has over 20 years experience in the industry.