Canadian shoppers are more likely than ever to be considering an all-wheel-drive (AWD) car or crossover as their next vehicle – and automakers are responding by launching more and more AWD-equipped models than ever.
Sales of AWD cars and crossovers are gaining traction, and with the influx of more AWD models to meet shopper demands comes numerous terminologies to understand. Below, we’ll look at a few of the more common terms in the world of AWD, and what they mean.
A differential is a mechanical component used in many vehicles, including AWD vehicles, that effectively “splits” drive power. In simple terms, drive power is delivered to a differential via a rotating driveshaft, and the gears within the differential split that power two ways. For example, think of a basic rear-wheel-drive vehicle: the differential takes a single input (drive power from a single driveshaft), and splits it two ways (driving each of two rear wheels).
Differentials can also be used to split drive power between two axles. In an AWD vehicle, a differential may be used to split drive power between the front and rear axles, with additional differentials used at each of those axles to split the supplied power again, between both wheels.
Sometimes, a differential is simply called a “diff”.
Torque Split / Power Split
These terminologies are complex and not relatively well understood by the average shopper – but they reference the “split” of drive power that’s available in a given AWD system. For instance, some AWD systems provide 50 percent of the drive power to the front axle, and 50 percent to the rear, for a 50:50 torque split. Others provide, say, 80 percent of the drive power to one axle, and 20 percent to the other.
Numerous factors, including available grip on any given surface, vehicle speed, and AWD system design, affect the torque split or power split that an AWD system is capable of.
Limited-Slip Differential (LSD)
An LSD is a type of differential that uses one of several means to reduce slippage between the vehicle’s wheels. With a standard differential, when one wheel is on ice, and the other is on bare pavement, the wheel with less traction tends to spin freely while the wheel with grip stays stationary. This is sub-optimal, so some vehicles use an LSD to reduce or eliminate this slippage, ensuring both wheels at a single axle participate in propulsion at all times, to generate more traction and grip.
Slip-and-Grip / Slip-then-Grip
These nicknames were given to certain AWD systems by enthusiasts, and they refer to an AWD setup that requires some amount of wheel slippage before engaging all-wheel traction. In older and more primitive AWD systems, a sometimes-excessive amount of wheelspin was required at one axle before the other was engaged, hence the term. Today, most AWD systems have evolved to provide full traction straight away on slippery surfaces, meaning that most modern AWD systems don’t fall into this category.
Power Take-Off Unit (PTU)
This is another AWD driveline component used in certain systems, and not others. In simple terms, the PTU facilitates the mechanical connection between the front and rear axles of a vehicle. It works by connecting the front and rear axles to drive power, using a clutch to engage and disengage the flow of power to one of the two axles when required, typically at the direction of an on-board computer. In simplified terms, a PTU accomplishes a similar goal to a differential, but works in a different way.
Mercedes-Benz’s all-wheel drive system is dubbed 4Matic. A broad umbrella term, 4Matic references any of at least five different AWD systems, each with different layouts and feature sets selected for the application in question. 4Matic is on offer in most Mercedes models, ranging from SUV’s to crossovers to compact cars to high-performance AMG models.
4Motion is the marketing name of Volkswagen’s all-wheel drive system. The current version of the 4Motion system represents the latest in an ongoing evolution from earlier systems, and uniquely includes compact and cleverly packaged componentry housed almost entirely in the vehicle’s rear axle. Recently, Volkswagen has expanded the number of models in which their 4Motion system is available. With the exception of the Volkswagen Touareg, the VW 4Motion system uses an identical construction and layout concept in every VW model to offer it – from the Golf R to the Alltrack to the Atlas.
This is the marketing name used by Audi for vehicles equipped with any of their AWD systems. Quattro AWD can take various forms and layouts, depending on the vehicle in question. Put simply, when considering an Audi, Quattro means AWD.
Mitsubishi’s all-wheel drive system is dubbed Super All-Wheel Control, or S-AWC. Made famous by the discontinued Mitsubishi Lancer Evolution performance car, the S-AWC has no fewer than three application-specific versions. Unique S-AWC attributes include a close tie-in with other vehicle dynamics systems, including braking, and the use of driver-selectable modes that enable fine-tuning to current driver demands and traction levels.
This is the marketing term for Subaru’s AWD system. The word “symmetrical” designates the layout and arrangement of the components of the system – which are arranged symmetrically within the vehicle’s powertrain, ensuring optimal weight balance. Look at Subaru’s AWD system in a top-down cut-away image, and you’ll notice it’s completely symmetrical.
BMW’s all-wheel drive system is called xDrive. Like the 4Matic or Quattro systems offered by its rivals, the xDrive designation is an all-encompassing term that describes the AWD system used in numerous BMW models, from compact cars to SUVs to high-performance models. With at least two distinctive hardware layouts and numerous enhanced functionalities, the xDrive system is arranged and engineered precisely on an application-by-application basis.
Many enthusiasts talk about Haldex AWD. In fact, Haldex supplies a multitude of automotive components to many manufacturers around the globe. Among their products are brake parts, suspension components (including popular Monroe Shocks), power steering pumps, cooling system parts, valves, control systems, pumps, and more. Haldex Traction was once a division of Haldex that supplied AWD systems to numerous manufacturers from Volvo to GM to Lamborghini. In 2011, Haldex Traction was acquired by BorgWarner, another major automotive supplier. Translation? Haldex AWD simply references the original supplier of the AWD system in question.
This refers to a type of differential, called the Torsen differential, which has a special design that helps optimize traction. Torsen stands for Torque-Sensing.
In a Torsen differential, a difference in rotation speed on only one side of the differential’s output causes special gears within to be locked together mechanically, until the speeds are equalized. This is a purely mechanical system, and works without electronics or any sort of clutch.
For example, some versions of the Audi Quattro AWD system use a Torsen diff to split drive power between the front and rear axles. If the rear axle experiences wheelspin and the front axle doesn’t, the difference in speed between the two axles causes the Torsen differential to lock up right away, impelling both axles to spin at the same speed, regaining traction. When traction is restored, both axles spin at the same speed, and the differential operates as normal.