What is Four-wheel drive?
Four-wheel drive, also called 4×4 (“four by four”) or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand and is typically linked via a transfer case providing an additional output drive shaft and, in many instances, additional gear ranges.
A four-wheel drive vehicle with torque supplied to both axles is described as “all-wheel drive” (AWD). However, “four-wheel drive” typically refers to a set of specific components and functions and intended off-road application, which generally complies with modern use of the terminology.
Most vehicles are two-wheel drive (2WD or 4X2). That means the engine’s power is only sent to two of the four wheels. This will be either the two rear wheels (rear-wheel drive) or the two front wheels (front-wheel drive).
How does this affect the vehicle’s performance? In slippery or off-road conditions, two-wheel drive vehicles can lose traction more easily. For example, one or both wheels could lose traction in heavy rain. In this situation, the front wheels can’t help—they’re not powered by the engine. This could cause a major problem.
In a four-wheel drive vehicle, it’s easier to maintain traction and control of the vehicle. If one or two wheels lose traction, you still have two or three powered wheels to keep you moving. This is very useful in slippery or off-road conditions.
Many four-wheel drive vehicles are actually part-time four-wheel drive. This means that, under normal conditions, the vehicle only sends power to two wheels. If a four-wheel drive is needed, the driver can switch with the press of a button.
Four-wheel drive vehicles haven’t been around forever. They became popular when Willys built the first Jeeps® for the United States military during World War II. Later, Willys made the first four-wheel-drive vehicle for non-military uses when it created the CJ-2A in 1945.
How Does a Four-Wheel Drive Work?
When 4WD is engaged, the engine sends power to the transmission, which is then split into the front and wheel axles. The torque gets transferred to the wheels, but the wheels must have traction on the road in order for the vehicle to move anywhere. Otherwise, the tires will merely spin as you have probably experienced when stuck in mud or sand.
Let’s say that you get your rear wheels stuck in the mud. If you have two-wheel drive (2WD), then your wheels will probably spin and spin. In this case, it might be extremely useful to have four-wheel drive so that your front wheels could get some traction on the road. If power was transferred to the front wheels, where the traction is, you’ be able to successfully get your car out of a sticky situation.
This is essentially what four-wheel drive does. It gives you traction where and when you need it. Although 4WD is a bit more complicated than that, it’s essentially a way to increase traction and power on the road.
Most of the time, all you need is 2WD. 2WD is used for regular road driving. When you need extra power and traction (deep mud, soft sand, ruts, steep inclines and declines, rocky surfaces, etc.), you can engage 4WD by pressing a button. The process for engaging 4WD, however, depends on your vehicle.
When to Use 4WD?
Four-wheel drive is generally ideal for rough roads, snowy conditions, and other off-roading scenarios. Typically, only off-roading enthusiasts need 4WD, although 4WD can help with heavy-duty towing and hauling. A vehicle equipped with 4WD usually offers three modes: 4H, 4L, and auto. Here’s when you should and should not use these modes.
4H (High)
When your 4WD system is set to 4H, you can drive fast, but not too fast. Most automakers suggest keeping the speed at 55 MPH or less. With 4H, you gain more traction on icy, snowy, muddy, and rocky roads.
For instance, you might want to shift into 4H if you’re driving on a snow-covered road that leads to a ski resort. Typically, you’ll switch to a 4H mode more often than 4L mode.
4L (Low)
In 4L mode, you should slow down, not speed up. Turn to 4L when you’re trying to get your vehicle out of a tough spot, such as moving through an extremely muddy creek bed, going up and down rock formations, splashing through water, or motoring through heavy sand. Think about it this way: When you need maximum traction and power, low and steady win the race!
Auto (Automatic)
Auto mode delivers a hybrid of four-wheel drive and two-wheel drive.
When set to Auto 4WD, your vehicle will automatically switch from 2WD to 4WD when needed. In 2WD mode, the vehicle will send power to either the front or rear wheels. If the system detects road conditions that require 4WD, like a slick, treacherous slope, it’ll shift automatically to 4WD. Power then goes to all four wheels, alternating between the front and rear axles to match driving conditions.
Rules Of The 4wd Road
The chief rule of the 4WD road is? Use it or lose it. Your 4WD system will deteriorate if it goes unengaged for a long period of time. Seals will dry out and gears will get sticky. Engage your 4WD every few months to keep it in working order.
- Don’t use 4WD on dry pavement. Avoid engaging 4WD when driving on flat, dry road surfaces. Your fuel efficiency will take a hit, along with your drivetrain.
- 4WD does not help you brake. Be careful! You will not gain braking ability or stability when braking through turns with 4WD. 4WD often contributes to overconfidence in drivers and can lead to accidents.
- Follow your vehicle manufacturer’s instructions for 4WD. Improper use of 4WD can break the front axles, shear the differential gears, and break apart the differential case (differentials give power to your wheels and allow them to rotate at different speeds). Car lingo aside, refer to your owner’s manual for 4WD guidance related to your specific make/model. The process for engaging and disengaging 4WD varies from vehicle to vehicle.
Advantages of Four-Wheel Drive
The main benefits of 4WD are traction and power. Have you ever seen those commercials where the Jeep is climbing over boulders and rocks? That’s 4WD in action.
If you are climbing a steep hill or are off-roading, you will want increased power in order to get over obstacles and climb steep hills. While 2WD will get you over even the steepest hills of San Francisco, if you are off-roading, you will probably want the extra power that comes with 4WD.
- 4WD improves traction in dangerous driving conditions, such as snow, ice, rocks, and other scenarios that can make control difficult. By engaging both sets of wheels, traction, and control improve.
- The additional weight contributes to a better grip on the road.
- 4WD is great for those who like off-roading.
If you frequently drive in conditions where there is low traction, or if you enjoy off-roading, you will greatly benefit from four-wheel drive.
Disadvantages of Four-Wheel Drive
In most cases, 4WD is not necessary. It uses more fuel and can also lead to overconfidence, leading to more situations where you can get stuck. Save money and fuel by only using 4WD when you need it.
- The main disadvantage of 4WD is added cost of purchase, maintenance, and fuel. The extra equipment (differentials, transfer case, etc.) adds complexity and weight to the vehicle, increasing initial market value, tire wear, and the cost of repairs and maintenance.
- The added power and weight of 4WD and AWD systems require more fuel, making them less efficient than their 2WD counterparts.
- Added weight improves traction and control, but it also increases the braking distance required to make a complete stop. Lighter vehicles can avoid collisions easier than heavier vehicles.
- 4WD and AWD can cause overconfidence in drivers, ironically leading to more situations where you can become stuck.
- Although 4WD improves traction, slow down and use extreme caution on icy, snowy, and slick roads. Overconfidence can lead to dangerous accidents.
