A short guide on the basics of 4WD and AWD for photographers.
It may surprise some, but I am a huge automotive enthusiast that works auto shows. The idea for an article about four-wheel drive systems arose from my daily interactions at work. Confusion over the smorgasbord of marketing terms describing four-wheel drive (4WD) tops the list of questions. It’s followed closely by understanding the actual need for such a vehicle.
I am considering trading my beloved front-wheel-drive workhorse for one with extra drive wheels since shifting into landscape photography. After all, who doesn’t like traveling off the beaten path? But is a 4WD like a Jeep Wrangler necessary? Or can the average AWD car fit the bill? Let’s explore our options!
Four-Wheel Drive, All-Wheel-Drive, Oh My!
What is the difference between Four-Wheel Drive (4X4) and All-Wheel-Drive (AWD)? Are they the same? Don’t they use the same parts? The answer is – yeah, well, kind of, not really.
Let’s start with the traditional four-wheel drive, also known as 4X4. This is the term used regarding trucks and traditional SUV’s. All four wheels receive equal power. Great for navigating rough and uneven terrain, but not great on-pavement. When making a turn, the inside wheels turn slower than the outside ones. If power delivery cannot adjust, a wheel hop or chattering occurs. Also, damage to components can occur at higher speeds.
Enter the two-speed transfer case! The “high” setting compensates for the rotational differences. This makes the system ideal for on-road conditions, higher speeds, and inclement weather. Meanwhile, the “low” setting lets you navigate those tougher trails. The addition of center differentials and limited slip differentials mitigate the awkward wheel hop issue further. More on that topic later!
AWD-I, S-AWC, Intelligent AWD, 4Matic, 4Motion, Quattro, x-Drive – Yikes!!
Forget all these marketing terms, as they mean the same thing. All-wheel-drive (AWD) is an evolution of the 4X4. We entered the era of all-wheel-drive vehicle control systems when they became more sophisticated.
AWD is optimized for high-speed and all-weather performance and not necessarily intended for off-road. The basics parallel 4X4 with full-time (all wheels engaged) and part-time systems (where the axle disconnects, so the car is 2WD until 4WD is warranted). Most manufacturers use the part-time system for one simple reason – fuel economy. Additional drive wheels create more parasitic drag, which increases fuel consumption.
Advancements in computer technology allow precise control over the AWD system. The vehicle’s various sensors determine when extra power is warranted. Within milliseconds, the transfer case engages and torque is delivered to the other wheels.
Engineers further program these systems to operate all wheels in specific conditions, such as temperatures below freezing or rain. Performance-oriented vehicles engage the AWD in “sport” mode, allowing optimal take-off traction.
Subaru’s Symmetrical AWD
An exception to the rule above is Subaru’s Symmetrical AWD system. Mounted inline, Subaru’s All-Wheel Drive provides a transfer of torque with minimal drag and power loss. This system does not rely on sophisticated electronic components to engage; adding to the reliability of this full-time AWD setup.
Locking Differentials and 2WD Capability
Do you need a four-wheel drive vehicle? Let’s look at a twist ditch scenario. When one wheel is off the ground, it freely spins since power travels the path of least resistance. Is the truck stuck? Not if equipped with a locking differential. Locking differentials, such as the “Eaton G80” will lock the axles together. This allows up to 100% of the available torque to be directed to the wheel that needs it. The downside to “lockers” is that they suffer around turns and on icy conditions since they cannot adapt for the rotational differences.
A second option is a limited slip differential. Limited slip differentials improve 2WD performance, just as they enhance 4WD performance. Since they don’t lock, limited slips provide better on-road performance, but in a real tough situation, such as this ditch, could leave you stuck.
The next best thing to “there’s an App for that,” is there’s a button for that! Traction control has become an art these days. The systems are so sensitive and quick to react that manufacturers have developed ways to tweak the algorithms to assist you in a variety of situations further.
Using Jeep as an example, the Select-Terrain System manages traction to give you all-weather capability in four modes: Auto, Snow, Sport, and Sand/Mud. The Trailhawk models take it a step further with a Rock mode. While there are many variations based on model and options, here’s a basic run-down on what happens with each setting, using a Jeep Grand Cherokee as the example:
This is the default mode. The front wheels receive 45% of the power, while 55% is sent to the rear.
The transmission starts off in 2nd gear, and more torque is sent to the front wheels.
Only selectable in Low Range, this setting will give you the maximum traction for those low speed, technical obstacles. On the Grand Cherokee, it also raises the air suspension 4 inches
Similar to snow mode, but the transmission starts off in 1st gear. More torque is sent to the front wheels.
This mode biases the rear wheels, up to 80%, for a more sports-car-like feel. The traction control is turned off, and the air suspension lowered. The transmission will shift quicker, as well.
Now Jeep is not the only one with a trick selectable traction management system. Many others are incorporating fun at the push of a button!
What Makes for a Great Off-Road Machine?
The fender of virtually any new Jeep wears a “Trail Rated” badge. Jeep introduced this designation in 2004 models to promote their vehicle’s off-road performance. While Jeep does own the trademark on the term, they use the Nevada Auto Testing Center to test their models in places like Northern Michigan, and actually drive them over the Rubicon Trail, a 22-mile-long route that’s part road and part 4X4 trail over the top of the Sierra Nevada.
Jeep tests the vehicles for their trail worthiness based on five categories – traction, water fording, maneuverability, articulation, and ground clearance. It’s a worthy concept for rating a 4X4 or AWD vehicle. So let’s break these terms down. You can use these as guidelines for gauging what you think you’ll need for your adventures.
Traction, the central theme of this article, is the ability to keep you on your intended path. Four-wheel drive optimizes traction. Electronic systems such as traction control, stability control, roll-over mitigation and ABS further enhance traction abilities.
Water Fording is the ability to traverse across water without taking it in or damaging the engine. Off-road vehicles utilize better weather sealing, and they position electrical connections and air intakes higher to enable driving across a body of water up to 19″ deep. This changes with additional options such as a lift, or a snorkel. The 19″ depth serves as the base requirement to earn this endorsement.
Maneuverability is the ability to safely navigate terrain, dodge obstacles, or pass through narrow gaps. Relevant factors include a shorter wheelbase, tight turning radius, and precision steering.
Articulation refers to suspension flexibility and the vehicle’s ability to keep stable address when one or more wheel is off the ground. Ground clearance and suspension travel are essential here. Specific models, such as the Jeep Rubicon, incorporate a disconnecting sway bar allowing additional suspension travel.
Ground Clearance is the ability to drive over rough terrain and rocks without damage. The angle of approach, break-over, and departure angles are maximized in off-road vehicles. Underbody skid-plating further protect critical components.
Beyond 4WD – Tires!
Often overlooked are tire choice and tire wear. Both subjects are incredibly important. These rubber components transfer power to the ground and move you. They are the only things sitting between you and the road. All the traction devices in the world mean nothing if the vehicle is riding on improper or bald tires.
Tire Application Choices
Specific tire applications use different compounds and tread patterns. Summer, Winter, All-Season, and All-Terrain are just a few of the choices. When looking for tires for your 4X4, you might want to determine the most extreme conditions that you will be driving through and pick tires to match.
Summer vs. All-Season
Summer tires should more accurately be called “three-season tires.” If you live in a climate that gets colder weather and you plan on using the same tires year-round, then a summer tire is not going to be a good choice. You may want an All-Season tire. You can tell if your tires are rated for All-Season by the “A/S” designation molded into the tire sidewall.
For winter driving, the softer compounds and deeper grooves found in snow tires perform well in low temperature, low traction situations. This increases the contact patch of the tire to the road surface. A 2WD car equipped with snow tires can outperform a 4X4 or an AWD car with summer performance tires, which illustrates the power of proper tire choice.
Winter tires are marked with the “Mud and Snow” designation “M+S” or they have the newer “Mountain/Snowflake” symbol. Like the A/S All-season mark, these symbols are molded into the sidewall of the tire. In some areas of North America, Mountain/Snowflake rated tires are mandatory for winter months.
I can vouch for how well winter tires work. The snow tire equipped Eagle Talon pictured at the top of this article, coupled with AWD, was an absolute tank. I should have never sold it.
All Terrain Tires
If you are going to be taking your 4X4 off-road, you want a tire that’s going to hold up to the wear and tear of driving over rocks or through sand. Not all Mountain/Snowflake rated tires should be used during summer months as the rubber compound is too soft for summer temperatures. Some like the BFGoodrich All-Terrain T/A KO2 tire can endure year-round service. It’s got an aggressive tread, protruding sidewall rubber blocks, and a rubber compound designed for both all-season road driving, off-roading, and overland travel.
If you plan on doing some low-speed rock crawling, you’re going to want some off-road maximum traction tires. And you’re getting beyond the scope of this article!
Tire Wear and Age
Worn tires significantly decrease stopping distance, traction, and cornering performance. The age of a tire matters, too. Rubber degrades over time and causes tires to crack and split, thus increasing the chance of failure.
For those of us who travel into cell phone dead-zones, the last thing you want is to get stranded! When checking tires, do not forget the spare! If going off-road, having a spare tire in good condition could mean the difference between getting home safely or not.
What Does This Mean for Photographers?
From the mundane daily commute to save-your-hide-in-sticky-situation drives, modern cars are engineering marvels. Honestly, most of us do not need a Four-Wheel Drive or All-Wheel Drive car.
However, for those considering modest off-road thrills, the assurance AWD and 4X4 offers you is undeniable. Any of the smaller SUV’s, and cars like Subarus, provide the capability needed for the average groomed trails. For those adventurers who want to travel overland on backcountry trails in slick rock country or climb mountains, that Jeep Wrangler with the Rock-Track 4X4 system is waiting for you. Go scale that mountain and snag that Milky Way badge!
To read more about various aspects of four-wheel drive systems, check out the following web sites:
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