4WD Explained : In the days of yore, 4-wheel drive and all-wheel drive were specialty items. Unless you owned a truck or an oddball vehicle such as an Eagle wagon or Audi 4000, your vehicle was two-wheel drive.Today, as crossovers and SUVs have knocked sedans off their pedestal as the default flavor of everyday transport, it’s also not unusual for any given car to have four driven wheels. But that doesn’t mean every system is equivalent.
Unless you’re equipped with a fully automatic all-wheel-drive system, you’ll have at least two selectable drive modes you can use to maximize your vehicle’s capability in a particular environment. If you drive something with off-road capabilities, like a Toyota Land Cruiser, you have more complicated choices — high range, low range, locked or unlocked center differential.
So, do you want 4-wheel drive or all-wheel drive? Off-roading? 4WD. Traveling to work through three inches of sleet? AWD becomes the hot setup in that case.In the early days of the SUV, four-wheel traction equated to 4-wheel drive. Most systems nowadays are all-wheel drive, which means that a center diff of some sort allows the front and back tires to spin at different speeds. AWD can work on dry pavement, while 4-wheel drive needs a slippery surface to allow for matching speeds in the front and back ends without binding.
Most modern crossovers are AWD and don’t allow you to disengage the system—they simply engage automatically, as necessary, if slip is detected. But even if you have that kind of system, there’s one thing you need to know.So if your vehicle has 2WD or 4WD Auto at its disposal, most of the time you might as well set it to the latter setting. It’s fine on dry pavement so the sole benefit to running in 2WD is either some fractional fuel economy gain—or preserving wear on the front-drive system. 4WD Auto is also great if it starts raining—your extra traction will always be there, on-demand, automatic.
If you have a system that has 4WD Auto, 4WD High is a pretty much useless setting. That’s because it simply locks the front and rear end of the car together; useful in some narrow off-road context, but doing nothing for you on that snowy road. In fact, most of the time off-road I’d rather the system sent power fore or aft as needed.
I had a friend who owned an all-wheeldrive late-70s Jeep Cherokee (so, 4WD Auto) and the only time he had to lock the 4wd system was when he attempted to drive through a pond that made the Jeep look like a primordial being crawling from the muckWithout an Auto setting, 4WD High is what you’d use in any situation that’s low-friction but moderately high-speed—a dirt
road or snow-covered paved roads. 4WD Low is only for creeping off road or situations where you need torque multiplication to get through where you want to go (like deep sand). Low used to be universal, but these days low is an option found only on pickup trucks and SUVs with serious off-road aspirations. A Toyota 4Runner will have it; a Highlander will not. OK, say you are
getting off road a bit—a little beach driving. This isn’t an off-road how-to but we’ll presume you released some air pressure from your tires. Good. And what the hell does that rocker switch on the dash do? The one that has four tires and a small “X” between the rears? That’s your rear differential lock, and it is useful.
Where 4WD High locks the front and rear axles together, the rear diff lock ties the rear end side-to-side. That means if one side loses traction, the other side continues to spin, propelling you forward. It’s a terrific feature, if you’re driving a straight line.