Some have differentials which allow left and right wheels and front and rear axles to turn at different speeds that can be locked for maximum traction. Modern 4WD systems are full-time, which means they stay engaged; automatic, where the vehicle automatically switches between two- and four-wheel-drive mode; or part-time, which requires the driver to manually shift between two- and four-wheel drive. Aside from serious off-road enthusiasts, most drivers never come close to needing the capability that 4WD systems provide over and above AWD systems.
Photo: Ford Photo: Ford. For rain and very light snow, 2WD will probably work fine, and for most vehicles, front-wheel drive is the preferred setup and is likely to cost less than an equivalent AWD model. AWD is fine for most normal snow conditions or for light-duty, off-pavement excursions on dirt roads or slippery surfaces. Keep in mind that both AWD and 4WD systems add considerable weight to a vehicle, compromising fuel economy. One of the reasons many people buy a traditional sport-utility vehicle is for the extra security and traction of four-wheel drive.
Though having power delivered to all four wheels increases straight-line traction, it does nothing to improve braking, and most systems have little to no effect on cornering. Drivers can be fooled into traveling too quickly in slippery conditions with an AWD or 4WD vehicle, only to discover they are going far too fast when trying to stop.
Because the added traction of 4WD can allow a vehicle to accelerate more quickly in slippery conditions, drivers need to be more vigilant, not less. Slippery conditions demand extra caution, no matter what you drive. In many cases, having good tires is more important than the drive wheels.
Photo: Acura Photo: Acura. Since , Consumer Reports has been testing products and working to create a fairer, safer, and healthier marketplace. Click here to learn more about Consumer Reports' mission as a nonprofit organization.
To help support our work, please consider making a tax-deductible donation. You can also show support by liking us on Facebook and following us on Twitter. We respect your privacy. All email addresses you provide will be used just for sending this story. How It Works: 2WD vs. AWD vs. By Consumer Reports. Most systems these days are AWD , meaning that there's a center differential of some sort that allows the front and rear tires to turn at different speeds. AWD can be used on dry pavement, where four-wheel drive requires a slippery surface so that the front and rear ends can match speed without binding.
Most modern crossovers are AWD and don't offer the option to disengage the system—they just work automatically, as needed, when they detect slip.
But even if you have that sort of system, there's something you need to know. If you've got a vehicle that offers two-wheel drive or four-wheel-drive auto, then most of the time you may as well use the 4WD Auto setting. It's fine for dry pavement, so the only advantage of running in 2WD would be some fractional fuel economy benefit—or saving wear on the front-drive system. Meanwhile, 4WD Auto is handy even if it starts raining—your extra traction will be there, on demand, automatically.
That's because it just locks the front and rear end together, which might be useful in some narrow off-road context but isn't doing anything for you on that snowy road.
In fact, I'd rather have the system sending power forward or back as needed most of the time, even off-road. I had a friend who used to have a lates Jeep Cherokee that was all-wheel-drive so, 4WD Auto and the only time he needed to lock the four-wheel-drive system was when he tried to drive through a pond that made the Jeep look like a primordial creature crawling from the muck. Without an Auto setting, 4WD High is what you'd use in any situation that's low-traction but relatively high-speed—a dirt road or snowy paved road.
Low range used to be common, but these days it's relegated to pickup trucks and SUVs that have serious off-road pretensions. A Toyota 4Runner would have it, but a Highlander won't.
OK, let's say you're venturing off-road—a little beach driving. This isn't an off-road instructional but we'll assume you let some air out of your tires. Now, what does that rocker switch on the dash do? The one that shows four tires with a little "x" between the rear ones? That's your rear differential lock, and it can be handy.
Just as 4WD High locks the front and rear axles together, the rear diff lock connects the rear end side-to-side. That means that if one side loses traction, the opposite side keeps spinning, powering you forward. It's a great feature, provided you're driving straight. You don't really want to use your diff lock on a corner, because the whole point of a differential is to allow your car to make a smooth turn, with the outside tire turning faster than the inside.
Lock them together and your car won't want to turn. Be sure to set your truck or SUV to 4H four-wheel drive. This way, you can drive at normal speeds when on the road. Remember, 4L simply means using lower gears in 4WD mode. This is not the case with 4L four-wheel drive, when you must slow down significantly or even stop.
Sponsored message: Rain or shine, protecting your truck from the effects of the weather just makes sense. While you can absolutely use four-wheel drive in inclement weather for highway driving, you should not use it when the highways are clear. As mentioned above, driving in high-speed with 4WD on means your wheels on both sides of the truck or car always turn at the same speed.
Fixing all those parts would be very expensive so ideally, you want to avoid using them unless you actually need to. Moreover, driving in 4WD mode means your engine is using more gas. It needs this to create enough horsepower to rotate four wheels — not just two. Generally speaking, 2WD has a better fuel economy.
This is ideal for when you feel driving conditions are getting unsafe. This is when you want to use four-wheel drive to navigate and avoid getting stuck. Again, check the video I posted above — the guy tests traction control as well 4WD modes.
Here are some ways you can stay safe and prolong the life of your truck or SUV when in four-wheel drive:. Thanks a lot, very useful. Just an FYI if you did want a 4runner. Thanks for this article. One other question. I have a Tacoma, TRD off road, and new tires, but on slick roads in 2WD it feels like it has little traction and 4WD feels much better — but 55 can be very low mph on highway.
Many articles say do not drive in 4WD over But that seems really low. Please let me know what think -if you can. Thanks for the comment, Jan! There are differing opinions about whether or not going over 55mph with 4WD enabled will cause damage to the 4WD system. If the roads are that bad, the majority of other motorists will likely reduce their speed as well. We hope this helps! The truth is, driving in the wrong mode at highway speeds absolutely could KILL you.
The power of any 4 wheeled vehicle comes from one engine to two or more wheels. Whenever the power needs to be split into two directions it needs to go through a differential to split the power into two separate drive shafts. There are three different basic types of differentials: locked, open, and limited-slip.
As you might have guessed, a locked differential locks the two wheels together in simultaneous rotation, while a open differential allows them to rotate independently of each other, and a limited slip differential allows some difference in wheel speed, but limits the ability for one wheel to travel faster than the other.
Locked differentials are absolutely the best type for off-roading over difficult slippery obstacles at low speed.
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