In recent years it has become increasingly difficult to understand the differences between AWD and 4WD vehicles. Manufacturers have shifted the boundaries and in the process blurring the line between the two. This is simply because both AWD and 4WD both have advantages and disadvantages and vehicle manufacturers are constantly trying to incorporate the best of both worlds into one desirable package.
In a traditional sense, AWD (All-Wheel Drive) means the vehicle has power sent to all four wheels on a permanent basis. 4WD (Four-Wheel Drive) means the driver needs to manually select 4H from inside the cabin to engage 4WD mode. Permanent 4WD constantly sends power to all four wheels.
With that being said, most people seem a tad confused with the differences between All-wheel drive and four-wheel drive since the modern four-wheel-drive and AWD have evolved and become so sophisticated over the last few years. This article will explain the fundamental differences between 4WD and AWD and the advantages and disadvantages of both.
Main Difference between 4WD vs AWD
The biggest physical difference between a 4WD and AWD is an All-wheel-drive does not have a transfer case or a locking center differential either. AWD vehicles also do not have low-range or rear diff lockers. AWD’s make use of clever electronic traction aids and wheel sensors. They also incorporate either a viscous coupling or a multi-plate clutch system.
The other major difference between 4-wheel drive and all-wheel drive is not always the transfer of power or traction but rather the driver interaction level which offers added control and higher safety levels. This can either play into your favor or against you, depending on what purpose you intend to use the vehicle for.
Almost 50% of vehicles sold in the United States are either 4WD or AWD
Manufacturers have cottoned on to this fact and almost all of them offer a version of 4WD and AWD in their range. This means there are additional features and technology they can use as a selling point to unsuspecting or ill-advised customers. They can also charge a lot more for vehicles with the aforementioned technology built in. Almost 50% of vehicles sold in the United States are either 4WD or AWD. This statistic means that vehicles with AWD and 4WD technology are viewed as more versatile, safer, and practical when compared to a front or rear-wheel drive vehicle and thus, are becoming increasingly popular.
There are basically two types of four-wheel-drive systems. A permanent 4WD and a non-permanent or part-time 4-wheel drive. Let’s look at the differences between the two now.
CAN YOU CONVERT A 2WD to AWD or VICE-VERSA?
Permanent 4WD
The term is almost self-explanatory since it means that the vehicle’s drivetrain is permanently in 4-wheel drive mode. Power is constantly sent to all four wheels irrespective of the driving conditions and surface traction. These types of vehicles can safely drive on dry pavements at any speed, highways, and byways and then hop straight onto a muddy trail or slippery surface without any driver interaction needed.
A permanent 4-wheel drive usually consists of a robust design and chassis. Most are built with a ladder frame chassis for added strength and rigidity when driving off-road. Most traditional permanent 4-wheel drives have at least one solid axle, usually the rear with the front an independent front suspension. This suspension setup offers a perfect balance between on-road driving manners and off-road capability coupled with good load-carrying ability.
(You can read more about the differences and advantages of monocoque vs ladder frame chassis here)
Permanent 4WD’s with ladder frame chassis are heavier than an AWD with a monocoque chassis, which plays into its favor when off-road conditions get tough or when towing. This is due to the fact that heavier vehicles can typically tow heavier trailers, boats, and caravans. The ladder framed permanent 4-wheel drive also increases the vehicle’s load-carrying capacity because of the chassis design and suspension setup.
Example
Below are examples of permanent 4-wheel drive vehicles:
- Land Rover Defender
- Toyota 4Runner Limited
- Toyota FJ Cruiser
These full-time four-wheel drives illuminate the need to shift between 2H and 4H and allow the driver to enjoy the freedom of driving on a variety of high traction and low traction surfaces without having to interfere.
Now let’s look at the part-time four-wheel-drive system.
Part-Time 4WD
Part-time or temporary 4-wheel drives are normally driven in the 2H mode where the power is sent only to the rear axle of the vehicle. This 2H mode is designed to be used for daily driving on high traction surfaces like tar roads and concrete pavements. The part-time 4-wheel drive drivetrain will function very similar to a rear-wheel drive when driving on-road and offers decent fuel economy.
With a part-time 4-Wheel drive the input of the driver is needed to convert the vehicle to a 4-wheel drive. This is achieved by selecting 4H from a short lever or dial inside the cabin which locks the front and rear driveshaft to function as one unit. This is at the discretion of the driver and should only be done when the vehicle is driving on a low traction surface where enough wheel slippage is possible. Failure to engage the 4WD system on a low-traction surface will result in serious drivetrain component damage and eventually drivetrain “binding”
Like a permanent 4-wheel drive, the part-time 4WD is in almost all cases built on a ladder-frame chassis. This gives it all the advantages off-road since the weight allows for improved traction in off-road conditions where surface traction is low. It also allows you to tow heavy trailers, boats, and caravans while driving off-road.
Semi-Permanent four-wheel drive is for drivers wanting the most rigid, robust, and capable off-road vehicle. These are used to travel long distances over rough, challenging road surfaces for extended periods.
Examples of part-time 4-wheel drive:
- Toyota Tacoma
- Toyota Tundra
- Ford Ranger
- VW Amarok MT
- Jeep XJ
Next, let’s look at the full-time or permanent All-wheel drive system and the pros and cons of it.
Full-Time AWD
Full-time All-wheel drive is a very sophisticated design that leaves very little manual driver interaction. The full-time AWD system basically takes care of all the power settings and allocates power and torque where it feels necessary. This allows the driver to just relax without having to worry about changing or locking anything diffs. The power is always sent to all four wheels irrespective of the driving surface traction. It accomplishes this by means of either a viscous coupling or multi-clutch systems or center differential which attempts to maintain traction by sending adequate power to either front or rear axles.
The function of the viscous coupling is to allow the front and rear axles to receive the required power needed to maintain traction by allowing the front and rear driveshafts to rotate at varying speeds. This is necessary when cornering on a high traction surface since the front left wheels and rear left wheels will be required to turn at slower speeds than the front and rear right wheels when turning left. The same applies when turning right, the inner right side wheels need to turn slower than the outer left side wheels and this is achieved by a viscous coupling.
Also, the front tires need to rotate faster than the rear tires since, when turning swiveling of the wheels means the front radius is larger than the radius of the rear tire. This means the front drive-shaft will be required to rotate at faster speeds to the rear driveshaft to accomplish this and this is achieved by the viscous coupling or by a multi-clutch plate system or a differential. This will allow the AWD to drive on a low traction surface like an icy road or mud track or on a high traction surface like tarmac road or cement pavement without any driver interaction needed.
(If you would like to read more about drivetrain binding and the effects – click here)
Viscous coupling
The viscous coupling is situated between the front and rear drive-shafts and consists of a series of plates rotating between each other in a thick fluid. One set of plates is connected to the front driveshaft and the other set of plates controls the rear driveshaft. Once traction is lost in the front wheels and the wheels start spinning faster due to loss of traction, the plates connected to the front driveshaft spins faster causing friction and that torque is transferred to the thick fluid to make the rear driveshaft also spin faster to catch up. This process sends power to the rear wheels via the rear driveshaft. The motion of the thick fluid between the plates causes torque transfer from front to rear resulting in the rear driveshaft spinning when the front set of plates turns faster than the rear set of plates.
It can be compared to a raw egg. If you spin a raw egg on a counter it will initially spin fast then quickly slow down and then continue to turn because the fluid and thick yoke inside the egg are still turning. I hope this explanation is understandable since it’s quite difficult to explain in the text without a visual aid.
I’ve inserted a video that explains the differences more clearly. Without my egg analogy … lol
Examples of Permanent AWD vehicles
- Subaru Forester
- Mitsubishi Lancer
- Renault Duster
- VW Amarok V6
Now let’s look at how a part-time AWD vehicle functions
Part-Time AWD
A Part-time AWD drivetrain functions like a front-wheel drive or a rear-wheel-drive vehicle since the power is always sent to either front or rear wheels until traction is lost. Let’s look at how this is achieved by means of the multi-plate system.
Multi-Plate Clutch system
It usually makes use of a multi-plate clutch system combined with a clever onboard computer and wheel sensors. The wheel sensors monitor front and rear wheel rotational speeds and send signals to the onboard computer. When traction is lost, the computer will attempt to synchronize the front and rear wheels by activating the multi-plate clutch system to bring them back to the same rotational speeds.
This is usually achieved by temporarily “connecting” the front and rear driveshafts. This is a temporary connection and once the computer recognizes that traction has been regained and the front and rear wheels rotational speeds are back in sync it will disengage and revert back to either front or rear-wheel-drive mode.
The multi-plate clutch system and the viscous coupling might sound as if they function the same, however, they are distinctly different in design and function. Viscous coupling is always engaged and usually incorporated in permanent AWDs. A multi-plate clutch system, on the other hand only activates once traction is lost in either front or rear wheels then deactivates to allow the vehicle to operate as a 2WD vehicle again.
This has a fuel efficiency advantage since there are fewer drivetrain components that are functioning to propel the vehicle forward.
Example of automatic AWD vehicles
- Honda CRV
- Ford Focus RS
- Mini All4S
- VW Syncros
4-Wheel Drive advantages over AWD
So now that we know the differences between 4-wheel drive and all-wheel drive as well as the permanent and part-time variations, let’s now look at the advantages of a 4-wheel drive over an All-wheel drive vehicle.
We will next discuss the rugged and robust structure advantage of a 4-wheel drive as well as its ground clearance.
(Read a more in-depth article about monocoque vs ladder frame chassis)
Rugged Structure
Most 4-Wheel drives have a body-on-frame or ladder frame chassis structure. This consists of two thick, reinforced, galvanized, metal beams that run in parallel and are joined together by smaller horizontal beams in-between, visually representing a ladder. This gives the 4WD ladder frame chassis strong stiff and rigid characteristics. A huge advantage over an AWD in challenging off-road conditions.
This is, however, quite an archaic structure and was originally implemented in the first cars ever built in the Ford Factory. Engineering and vehicle technology has progressed a long way since, yet the ladder frame still lives on. This is largely due to 3 factors:
- Robust Framework
- Rigid structure
- Off-road Superiority
Most SUVs, UTE’s, Commercial trucks incorporate the ladder frame chassis to allow them to carry heavy loads for extended periods. A 4WD with a ladder frame is perfect for off-road conditions.
All-Wheel drives, on the other hand, are mainly developed with monocoque chassis that incorporate more modern safety features. The modern monocoque chassis found in AWD vehicles are very advanced and offer a host of advantages over the ladder frame derivative. The monocoque structure is when there is no separation between the body and the chassis as in the case of a ladder frame, but rather the entire framework is integrated into the body construction, making it one complete structure. This allows manufacturers to incorporate crumple zones and reinforce other areas of the cabin to make the vehicle safer in the event of an accident.
The monocoque structure found on most AWD’s offer the following benefits:
- Weight reduction
- Ride dynamics
- Improved safety
- Lower production costs
There are a few disadvantages to AWD with monocoque chassis too. Those include low ground clearance compared to 4WD vehicles, being more prone to undercarriage damage when going off-road. Repair costs are also very high since the monocoque requires advanced laser welding and cutting to repair.
Monocoque chassis on AWD’s are more prone to rust and moisture damage when exposed to water or snow often with critical drivetrain components being lower down and more susceptible to damage.
Ground Clearance
The ground clearance of a 4-wheel drive is far more superior to an AWD and can easily be upgraded to be even better. This is largely due to the above-mentioned ladder frame chassis designs which allow easier suspension upgrades. Ground clearance on a standard 4-wheel drive can easily be in the region of 200mm and above which makes it ideal for off-road conditions, even in stock form in many cases.
if you would like to read about the minimum ground clearance required for off-road click here
All-wheel drive ground clearance is substantially better than a 2WD vehicle but not as good as a 4WD. AWD suspension upgrades are limited since in most cases they have independent front and rear suspensions which limit you to how high you can increase the ride height. Aftermarket suspension upgrades are limited for AWD vehicles since they spend most of their lives on tarmac roads.
AWD’s are thus more suitable for light dirt roads, ice, and snow-filled tarmac roads, and shallow sand tracks. Where driving conditions are not too challenging in terms of uneven surfaces and large boulders or deep ruts to overcome, but where traction is limited, this is where an AWD will thrive. AWD is ideal in mixed traction roads where some parts of road surfaces are high traction and other parts are slippery since the driver’s input is not needed and everything is taken care of by the AWD system. There is never a risk of drivetrain binding on an AWD.
More Control
The best thing about an AWD is that there is no driver input and everything is taken care of automatically by the AWD system.
For a true 4-wheel drive enthusiast, however, that is not an advantage since a vehicle that can be totally managed and manipulated by the driver’s input is what most 4-wheel drivers desire. Also, when venturing into remote parts of the country where mechanical assistance is usually days away, you require a more robust, basic reliable design with less complex electronics to malfunction.
A 4-Wheel drive in a sense gives the driver more control over a variety of surfaces and road conditions than an AWD. The driver can choose between 2H – 4H – 4Lo, Diff locked, Diff open, depending on the driving conditions. A 4WD can essentially drive everywhere an AWD can go with ease and then do some even more challenging hard-core off-roading.
Load Carrying abilities
Here the 4WD with a ladder frame stands head and shoulders above the AWD since the ladder frame chassis combined with solid axles and leaf packs in the rear makes for a really robust design. This affords the 4WD to carry really heavy loads on bad road surfaces for extended periods without fail. The rigid design of the body on frame combined with its excellent ground clearance due to the ladder frames high floor plan makes the 4-wheel drive the ideal off-road mobile.
Let’s now look at areas where the AWD will thrive and easily outshine the 4-wheel drive setup.
AWD Advantages and Disadvantages over 4-Wheel Drive
Ease of use
An AWD has some clever electronic traction aids built-in which make use of smart software built into the AWD management system. The vehicle maintains traction by receiving data signals from wheel sensors which are sent to a computer to manipulate the drivetrain to maintain traction. The front and rear drive-shafts work together with an adjustable torque distribution coupling or clever multi-clutch system to regain traction.
This design makes driving an AWD very easy in a host of slippery low traction environments where ground clearance is not a concern. All of this is achieved with zero driver input. The driver can, however, select how much power is distributed to the front and rear axles from inside the cabin. This will change the vehicle driving dynamics to be either be more rear wheel is driven, front-wheel drive, or 50/50 split. No 4WD I’ve ever heard of has this functionality built-in yet. Even with this technology, the AWD is not popular among hard-core off-roaders.
This stance is changing rapidly since the lines are being skewed with off-road utes now being developed with full-time AWD which also has off-road capabilities.
A prime example of this is the latest VW Amarok v6 4motion. Just like and AWD, It has no transfer case. It does, however, like a 4WD, incorporate a low-range crawler gear which is 1st gear, and some clever traction electronics like an AWD. It also has traction control and rear diff lockers like a 4WD. It cannot, however, lock the center differential, like an AWD. It is built on a ladder frame chassis, like most 4WD’s. The best part is, it drives everywhere an AWD and a 4WD can with ease.
So it’s essentially a hybrid between an AWD and a 4WD. The lines don’t get more blurred than this…
AWD vs Front-Wheel Drive
An AWD has many advantages over a Front-wheel drive vehicle, especially the part-time AWD. This is because it offers the driver the ability to comfortably drive on slippery road surfaces and other low traction environments with ease of use and very little driver input required. Part-time AWD also delivers decent gas mileage since it only drives in front-wheel-drive until the moment traction is lost. Within split seconds, the multi-plate clutch system engages the rear wheels to regain traction with virtually no lag time. When this occurs the driver hardly notices any changes in the vehicle’s behavior. The Honda CRV Real-Time AWD system is a prime example of this functionality.
AWD vehicles also have a slightly better ground clearance and shorter overhangs to FWD (front-wheel drive) vehicles since it is designed to do light off-road work. Dirt roads, muddy tracks, and slippery snow is no match for an AWD where a FWD will be lacking in traction and control.
With a part-time AWD, you have all the benefits of an AWD when needed and the fuel efficiency of a front-wheel drive under normal driving conditions.
Best All-Wheel-Drive Vehicles
Let’s look at a few popular AWD vehicles that have led the race over the years with cutting-edge technology and drivetrain system designs.
Subaru Symmetrical AWD system
The Subaru Forester must be one of the best AWD vehicles produced to date. Most Subarus make use of a Symmetrical All-Wheel Drive (AWD) system. This gives the vehicle a perfect balance and control. It’s a permanent or full-time AWD which means it sends power to all 4 wheels all the time.
The near-perfect symmetrical layout of the Subaru’s gives it almost perfect balance on and off-road. This gives it superior grip, balance, and control when you need it most.
Honda CRV Real-Time AWD
The Honda CRV is the perfect example of a part-time AWD vehicle since the vehicle is always in front-wheel-drive mode until traction is lost. At that instance, the real-time AWD system engages the rear wheels to regain traction in an instant. It accomplishes this with its multi-plate clutch system that connects the rear drive-shaft instantaneously to the front drive-shaft, converting the vehicle to an AWD. The rear wheels propel the vehicle along with the front wheels when the system engages AWD mode.
The Honda Real-time AWD system accomplishes its lightning-quick reaction time by means of an intelligent control system that incorporates an electric motor to engage the AWD system. This electronic system reacts so fast that it eliminates all lag commonly associated with traditional part-time AWD’s that use the mechanical multi-plate system which has noticeably delayed reaction time. Once traction is regained the Real-time AWD system disengages automatically and the vehicle functions like an FWD car again. This drastically improves the Honda CRV’s gas mileage compared to traditional AWDs.
Best 4-Wheel Drive vehicles
The four-wheel drives with the best reputation for reliability and robust build quality must be the Toyota Land Cruisers and Later Nissan Patrols. They offer comfort combined with unrivaled legendary reliability as well as impeccable off-road capabilities.
Jeep Wranglers have had a mixed bag of success over the years with the 2018 Wrangler probably being the most unreliable, problematic model of the lot. They still make excellent off-road vehicles due to their robust purpose-built design and unlimited customization options.
The Land Rover Defender has been the icon of off-road and over-landing for decades. It is arguably the most iconic name in the off-road industry. However certain TD5 models have been plagued by specific reliability issues that have now been well documented online and most have been resolved over the years. They offer a perfect platform for multi-day expeditions due to their square shape and almost fully customizable aluminum body.
Another vehicle worth a mention here is the Toyota Land Cruiser Troopy. Just like the Defender, it offers heaps of customizable space in the rear. Coupled with legendary Toyota land cruiser reliability, they make for an excellent off-road and expedition vehicle.
Conclusion
Which do I need? Well, that depends on what you intend on doing with the vehicle as well as which part of the world you live in. If you don’t intend on doing serious off-roading then an AWD will be better suited to drive on slippery road surfaces yet still offer decent fuel economy in city traffic. AWD is more suited to light dirt roads and mild off-road tracks where ground clearance is not a requirement.
4-wheel drives, on the other hand, open up opportunities to explore the most remote parts of your country with confidence. Load-carrying ability, Good ground clearance, and reliability are all prerequisites to purchasing a 4-wheel drive.