Four-Wheel Drive vs. All-Wheel Drive: What’s the difference?
By Sean P. Holman
While out exploring, you may have seen the signs that read “High-clearance, four-wheel drive only”, and then you might have been surprised to see Subarus or RAV4s further down the trail. National Parks have recently been in the news for threatening a $5,000 fine on adventurers who explore “four-wheel drive restricted roads” in all-wheel drive (AWD) vehicles.
We assume part of this is because of the cost associated with incapable vehicles and drivers finding themselves stuck far off the beaten path and the safety risk related with such things. Regardless it is always good to understand your equipment before you venture in the backcountry, so which system do you have and what’s the difference?
Marketing
The terms four-wheel drive and all-wheel drive technically are the same, however, marketing of these features have muddied the waters for most consumer’s understanding of the technology. Over time, and as marketing and vernacular has evolved, 4WD has become synonymous with off-road capability, while AWD has meant all-weather capability and on-road performance.
Four-Wheel Drive
Four-wheel drive (4WD) systems are the traditional system that you can find on everything from Jeep Wranglers to pickup trucks. Other vehicles that have true four-wheel drive systems, include Jeep Grand Cherokees, Toyota 4Runners, Chevy Tahoes, and Nissan Armadas. What separates four-wheel drive from AWD? Typically, it’s a two-speed transfer case and the ability to lock up at least one differential.
A transfer case is the gearing box that splits power coming out of the transmission and sends it to both ends of the vehicle. While both 4WD and AWD vehicles have transfer cases, 4WD vehicles have what is called “Low Range”, or a gearing reduction that sends more torque to the wheels, enhancing the ability to crawl over technical terrain at slow speeds. These are known as two-speed transfer cases (“High” is the normal gearing, “Low” is the secondary gearing), while AWD vehicles have single-speed transfer cases that lack a gear reduction function.
Out of the 4WD vehicles, there are typically two types of systems, full-time (which operates like AWD in its normal operation) and part-time. Full-time systems, like AWD systems, can be used on pavement and have a center differential that allows a differentiation in speed between the front and rear axles and can distribute power unevenly to the axle that needs it. This is no
different than axle differentials, which sit between wheels on the same axle, allowing the vehicle to turn by allowing an outside wheel to turn faster than an inside wheel around a turn.
Part-time systems typically cannot be used on hard, high traction surfaces like pavement. They revert to two-wheel drive in normal operation and can be put into “4-Hi”or “4-Lo” with a switch or lever. These settings lock the center differential, and therefore the front and rear driveshafts spin together at the same speed, which is why part-time 4WD shouldn’t be used on pavement. Some systems have an “Auto” function, which allows AWD-like capability on pavement where power is sent to the non-primary axle only when slip is detected.
Full-time and part-time 4WD systems are heavier and stouter and can be found on vehicles designed to be more robust and durable in off-road environments. The ultimate version of a true 4WD system adds locking capability to the rear AND the front axle. These systems are often rereferred to as being “triple locked” and in conjunction with the low-range gear set, the locked center, front, and rear differentials give the vehicle the most capability, especially when lifting tires in the air.
All-Wheel Drive
Because AWD doesn’t have a heavier two-speed transfer case, they are typically used on lighter vehicles, such as smaller crossover SUVs, like any Subaru, RAV4s, Jeep Compass Trailhawk, and pickups, like the Maverick, or Sprinter vans. Entry-level systems are designed to be on-demand, meaning the rear axle for example, is only engaged when the front wheels are slipping, and are not suitable for off-roading. More sophisticated systems are persistent in nature and are constantly reading road conditions and sending power to the wheels that need it most.
Some more advanced systems do allow the user to “lock” the AWD system to mimic high-range on a true 4WD system for increased control and some AWD vehicles even allow you to lock the rear differential, getting you even closer to 4WD performance, but in a lighter duty package. Don’t be fooled though, while these are very capable AWD systems, they still aren’t true 4WD. It is also important to note that most AWD vehicles lack true full underbody skid plating, ample ground clearance, and because of the lighter duty platforms, include less aggressive and tough tires.
Know Before You Go
So which system does your vehicle have? If your vehicle has AWD (sometimes marketed incorrectly as 4WD) badges on the tailgate, but there are no controls for the driver to manipulate, you most likely are driving an AWD vehicle. If your vehicle has minimal controls that include some sort of lock button for the drive system, but no low range setting, you have a more performance-based AWD system. However, if you are in a vehicle that has levers, buttons, or switches that show low range, and even better, the ability to lock the center, rear, or all three differentials, you are in a true four-wheel drive vehicle. If you still don’t know, be sure to consult your owner’s manual or the manufacturer.
With all of that being said, just because you have four-wheel drive doesn’t mean you are impervious to all trail conditions. Driving in the backcountry only starts with equipment, it is up to the driver to know how to manipulate that equipment to its level of capability. For the novice driver out here, many manufacturers now include set-and-forget drive modes, which can alter settings based on the terrain, but it will always be important to use common sense and know you and your vehicle’s limits.
