All-wheel drive is a type of four-wheel-drive system or mode that automatically shifts power between the front and rear wheels to maintain traction and is usually adequate for lighter-duty winter driving and light off-pavement use. Four-wheel drive can reasonably be used as an umbrella term for any system that powers all four wheels, but in the context of this-or-that, the term is often used to describe such a system or mode that excludes the properties of AWD and is heavier duty, meant for serious off-roading.
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The above description is the best we can do at this point in history, because the definition of AWD and any distinction between it and 4WD has become less ironclad as technology has evolved and people (and automakers) have begun using terms however they see fit. AWD is so different from how it started out decades ago s” and there are now so many exceptions even to my good-faith definition above s” that I suspect one or the other designation isnss long for this world, though it wonss go without a fight, like the long-obsolete term sścrossover.sť The best approach for consumers is to focus on what a vehicle and its features can do, not merely what theysse called.
Look around the internet (if you must), and youssl find explanations different from the one you see here s” some from smart people who insist that, if a system has a particular piece of hardware, its™s 4WD, and if it doesnss, its™s AWD. There was a time when it was that simple, when AWD and non-AWD were opposites in most ways, but those days are long gone. To grasp all of this better, it might help to understand what sśall-wheel drivesť originally meant, and how its™s changed.
No Intervention From the Driver?
When early AWD came along, most 4WD systems had to be turned on when needed and then off again when decent traction was restored, so one of AWDs™s big plusses was that it did the work for you s” so much so that there were no controls at all. That changed with the increasingly common AWD lock button that divides torque 50/50 between the front and rear axles, ostensibly for slippery surfaces. Wait, doesnss the AWD system already automatically compensate and shift power? Yes. Most AWD systems lack this button, and its necessity is indeed questionable. In whats™s usually considered an AWD system (the light-duty type), this button doesnss lock the front and rear axles together as solidly as an old-school 4WD system does; it merely pre-activates the same clutches that would otherwise react once underway and wheels start slipping s” but because its™s done beforehand, the lock is more reliable and it can help prevent unnecessary overheating of the center differential that might result as its clutches engage and release repeatedly while attempting to achieve the same ends: steady forward progress.
Many AWD systems now also have different modes, such as Snow, Sand/Mud, etc. Technically, these are traction-control modes, but even as I type this, I realize Is™m reinforcing my own argument that using underlying hardware to define AWD or 4WD rather than driver-facing features and capabilities is ridiculous. You buy AWD for traction and Is™m going to try to convince you that something called sśtraction controlsť is unrelated?
Light Duty and No Low Gear?
Without a doubt, if you wanted to do some real off-roading in the early years of AWD, what you needed was 4WD, because only 4WD had a transfer case with a low gear for hill climbing and rock crawling. Behold: the Dodge Durango, an off-road-capable relative of the Jeep Grand Cherokee and one of todays™s notable exceptions to that old rule. This might just be a marketing decision to call this system all-wheel drive rather than four-wheel drive, but once that startss¦.Beyond that, compact Jeeps for years offered a Crawl mode via transmissions with very wide gear-ratio spreads s” such as continuously variable transmissions. Is the proliferation of low gears in AWD systems around the corner?
A System, Not a Mode?
Perhaps it was part of the no-intervention ethos, but early on, AWD generally represented an exclusive system, not a setting that could be selected among others, such as a two-wheel-drive mode. That has changed, as well. The Cadillac XT4 is an example of a recent AWD vehicle that also operates as front-wheel drive (meaning the rear wheels donss engage even if the front ones slip) if the driver has chosen the Touring drive mode. Other vehicles are more explicit: For years, some versions of the Ford Expedition SUV and F-150 pickup have combined a rear-wheel-drive setting (2H, where H refers to the high gear) with a 4A (realistically, AWD or automatic 4WD) and a 4L (that low gear AWD vehicles arenss supposed to have). The F-150 Raptor, a pinnacle of heavy-duty off-roading, includes these modes and adds 4H (4WD high, which locks the center differential).
Purists may protest that 4A is not AWD but, rather, full-time 4WD. I could get into all the definitions of full-time, part-time and permanent 4WD, but its™s pointless, because theres™s no difference in the way a modern AWD and full-time 4WD system behave from the perspective of the driver: They both can be left on regardless of the road surface and operate automatically to transfer torque in less-demanding low-traction scenarios.
The Only Question That Matters
So what functional argument is left for the supposed distinction between AWD and 4WD? That AWD is for light applications only and Dodge should be publicly shamed for the Durango? Enter BMW, respected manufacturer of xDrive all-wheel drive, whose current M5 super sedan is another recent model that allows you to select rear- or all-wheel drive s” though the car itself calls it 4WD.
Whats™s the point? Theres™s plenty of confusion already, countless examples of why this confusion exists and theres™s sure to be more confusion to come as technology changes. The AWD and 4WD distinctions are barely effective today. Shoppers are better off asking not what the drive system is called or whats™s under the skin but rather what it can do.
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