Surely the thought of piloting a vehicle through the four months of Canadian ice and snow can put strange thoughts in your head. If, by chance, you’re looking for something with four driven wheels rather than two, the choices can be mind-boggling.

But what is the difference between 4WD and AWD? Not an easy answer. The number of available four-wheel-drive systems is long and varied, ranging from simple part-time systems to full-bore computer-controlled full-time all-wheel-drive. Choosing which system to purchase should be determined by figuring out what you want to be able to do.

Traditionally, four-wheel-drive as we know it is reserved for Jeeps and other off-road kings. In normal operation, these are rear-wheel-drive machines. But, when needed, a centrally mounted transfer case can ‘lock’ the front axle to the rear, splitting the torque sent to both axles evenly. In addition, most have a low-range gearset that could be engaged for when really roughing it.

The disadvantages are immediately obvious; when the transfer case locks, both axles are required to travel at the exact same speed. That’s perfectly fine when traveling in a straight line, but once some steering comes into play, the front wheels travel a different distance compared to the other, and the rears track their own path as well. When on a low-traction surface like a dirt road or snowy parking lot, the tires slip enough to make up the difference. However, when on a high-traction surface like dry pavement or concrete, because the tires slip very little, all that extra energy goes back into the system and creates binding or breakage.

As such, these 4WD systems are known as ‘part-time’ as they require a very special set of circumstances to be used properly without risking damage to the vehicle’s drivetrain. You can generally still find them on serious off-road-biased sport-utilities and pickups.

The major development in what is considered to be ‘set-it-and-forget-it’ four-wheel-drive was the adoption of a center differential between the front and rear axles. Just as a differential on an axle allows the two wheels on it to turn at different speeds, the center differential allows the two axles to turn at different speeds, eliminating the mechanical bind of a traditional transfer case.

These systems are generally recognized as full-time 4WD, but they still allow the vehicle to be switched between 2WD and 4WD, pretty much at will. However, what makes it even more confusing for the average consumer is that hear these systems referred to as part-time 4WD since all four wheels are not required to be driven absolutely all the time.

Most automakers also have their own naming scheme for whatever proprietary systems they have in place, like Jeep’s Selec-Trac and Control-Trac. This makes choices at the dealership difficult if you haven’t done your homework first.

The only real way to determine which system you’ve managed to order is by checking the vehicle’s manual. If it advises not to engage 4WD on a high-traction surface, then bingo: it’s the part-timer.

Now we come to the really fun part. Not long after adopting the centre differential, manufacturers started installing ‘automatic’ 4WD systems that would split torque to both axles when the driving wheels lost traction. The benefits were immediate: four-wheel-drive traction when stuck but less of a fuel-economy hit when the system isn’t needed.

To go further down this road of explanation, we need to discuss differentials a little more. In a part-time 4WD system, because of the open differential between axles, once one wheel has no traction to work with, the wheel sharing that axle will receive no power. But, despite the rear axle being locked to the front, as long as they have traction, the rears can still help get you out of sticky situations. However, on a full-time system with an open center differential, only one out of all four wheels needs to start spinning for the remaining three to stop turning. It seems counterproductive to pay all that money for a 4WD system that allows you to get stuck so easily.

There are remedies, though; first, you could equip your vehicle (if the option is available) with either locking or limited-slip differentials, which provide traction to the opposite wheel even if its mate is spinning uselessly.

The other trick would be to learn how to provide that spinning wheel with some resistance, usually by brushing gently on the brake pedal. That force is usually enough to leach some power into the opposite wheel, and you should be able to creep out. In fact, this is exactly what Mercedes-Benz ML-class vehicles use as a four-wheel-drive system: open differentials front, centre and rear, and an onboard computer uses ABS wheel sensors to detect slip, and triggers the brakes accordingly. Think of it as highly aggressive, permanent traction control.

Things get even more complex when comparing pickups and sport-utes versus cars, especially as the latter have (for the most part) done away with the manually locking center differentials found in early Audis and Subarus.

The relatively new segment of crossovers are designed to look like a traditional sport ute yet most are based on an already existing car platform, jacked up and fitted with some form of 4WD. Most times, the vehicle spawning the platform won’t even have 4WD as an option while the ‘estate on stilts’ will; I.E. Toyota Camry vs. Toyota Highlander.

Today, systems can generally be thrown into a catchall Automatic On-Demand (AOD) 4WD category, but most stick faithfully to the All-Wheel-Drive (AWD) description in their advertising and literature as it is simpler to convey.

The AWD ‘category’ now includes ‘true’ all-wheel-drive vehicles, like most Subarus and Audis, along with various Mercedes-Benz, BMW, Infiniti, Porsche and Volkswagen models, but also to those with AOD-style 4WD like any Volvo, Honda Pilot, Toyota Highlander, Chrysler Pacifica, Buick Enclave, any of Mazda’s SUVs, etc.

However, because the systems in these vehicles are as varied as their parentage, their ability to handle low-traction situations, or enhance performance in high-traction situations, is just as broad. The problem with the AOD vehicles is how quickly the systems respond between 2WD and 4WD – those with clutch-based centre diffs generally react quicker than those with pure hydraulics. Smoothness is key since transferring torque to the un-driven wheels in one big rush can also upset handling at the limit.

And as with full-time 4WD, some sort of locking or limited-slip differential is key to not getting stuck at the worst time.

As with anything, 4WD technology keeps improving at an astounding rate, blurring the boundaries even more between what were once fairly distinct sub-classes. The new systems in the BMW X5 and X3, the Infiniti G35x and M35x, and virtually the entire high-performance end of Subaru’s lineup, can be called ‘intelligent AWD’ since they almost continually shift the front/rear torque distribution based on a huge range of conditions, including vehicle speed, throttle position and cornering loads. Acura’s Super-Handling All-Wheel-Drive (SH-AWD), now seen on the RDX, MDX and RL, will not only split torque front to rear as it sees fit, but it can also route more torque to the outside-rear wheel while cornering. This helps speed that wheel up, ‘over-driving’ it compared to the inside wheel, assisting high-performance driving.

The easiest piece of advice was mentioned earlier: figure out what you need to suit your lifestyle, and focus on a vehicle that meets those needs. Then read your owner’s manual, and read it often. There you will find all the technical information you need to maximize the way your vehicle’s 4WD system operates.

Sometimes even the best-sounding system in the showroom can still leave you stuck in a rut.