Tuesday, August 2, 2016

The Difference Between 4Wheel Drive SUV's and All Wheel Drive Vehicles

I found this helpful information about the difference between a 4Wheel Drive(4WD) Truck and All Wheel Drive(AWD) car/SUV.

Despite the increasing number of online resources and shifting dealer strategies, car shopping is still a bother. Add in all the new car segments, vehicle features, and technology acronyms, and the process becomes truly daunting.

There’s a long list of confusing topics when finding the right car, but all-wheel drive (AWD) and four-wheel drive (4WD) seem to consistently confound salespeople and car shoppers alike. Often, these terms are used interchangeably, but are they really the same? In the motoring world, they actually refer to very different systems, which can produce radically different results. But let’s get to the point: how does 4WD or AWD impact your daily driving life, and which badge belongs on your car?

Four-Wheel Drive (4WD)

Lets start with the old-school version. 4WD, sometimes also referred to as Four by Four, or 4×4, is typically used on off-road vehicles – or at least vehicles with all-terrain capabilities.

Unfortunately, 4WD doesn’t fit neatly in a one-sentence explanation, but we’ll stick to the basics here.

Power goes from the transmission to what is known as a transfer case. This system then splits power between the front and rear axles so that maximum torque is going to each wheel. This power delivery process is nothing new, and still manages to propel modern Jeeps over, well, just about anything, but it does have some issues.

When the transfer case splits power evenly, it ensures that each wheel turns at the same speed. This is deeply problematic when doing things like turning. You see, for a car to make a turn, the inside wheel has to turn more slowly than the outside wheel, which is covering more ground. If the vehicle can’t do this, the inside wheel loses traction and it spins freely. This, as you might be able to guess, isn’t great for moving forward efficiently.

There are a couple of ways that modern 4WD systems get around this. For starters, most modern 4WD systems are only on when you activate them. This can be done electronically or by using that protruding lever that sits somewhere between your radio and the center console. That way, you can use 4WD at low speed in snow or mud, but enjoy the drivability of two-wheel drive in normal conditions. When left in 2WD, there are fewer moving parts, and therefore fewer restrictions to forward motion. Said a different way, you’ll save fuel when don’t need to engage 4WD.

The other, more refined 4WD systems are activated with buttons or switches, rather than a manual lever, and include multiple settings for the 4WD system. These systems usually have a 4WD ‘High’, which splits power less evenly and allows what’s called ‘limited slip’ between the inside and outside wheels. This corrects the locked, spinning inside wheel problem to a point. Typically, however, High 4WD is recommended only up to around 60 mph. Flip these into ‘Low’, and they act much the same as old, locked systems. You really don’t want to try moving quickly in 4WD Low…things start breaking.

4WD Pros4WD Cons
Best traction in off-road conditionsAdds weight and complexity to cars
Can be turned off to improve fuel economyCan’t be used in all conditions
Proven, rugged technologyMore expensive than two wheel drive models


All-Wheel Drive is a much more recent innovation, and, as you might expect, much more complicated. It crops up on everything from supercars like the Audi R8 to grocery-getters like the Buick Encore.

In fact, a good rule of thumb might be to think of AWD as the “car” system while 4WD is the “truck” system. In this rule, consider crossovers like the Honda CR-V, Toyota RAV-4, Mazda CX-3, etc. to fall under the “car” category while SUVs like the Chevrolet Tahoe and Toyota 4Runner fall under the “truck” category. To better understand the differences between crossovers and SUVs, check out this article.

The biggest difference between 4WD and AWD is that an AWD drive system is on all the time. Well, mostly. But we’ll get to that, as there are two types of all-wheel drive: mechanical and electronic.

The most common way of accomplishing a capable, mechanical AWD system is by using three differentials. A differential is a box of gears, a.k.a. engineering magic, that can take power from the transmission and split it at different levels between two wheels or the front and rear axles (four wheels).

In AWD, this system works to get power to the wheels with the most traction by splitting power between the front and rear axels on the center differential, and the individual wheels by way of the front and rear differentials.

This is useful either in slippery conditions when different wheels might be getting different amounts of grip from moment to moment. The Mercedes-Benz E63 AMG is a perfect example. It is now sold only in AWD in the United States because its power can overwhelm the traction of the rear wheels alone. But even when we aren’t talking about 500+ horsepower cars, splitting power evenly means added stability in all types of weather.

AWD isn’t quite as robust as 4WD and it can’t match the same levels of traction in extremely low-speed off-roading that the older 4WD systems provide. But AWD does have some clear advantages.

The pioneer and industry standard for AWD systems, Audi Quattro, distributed torque mechanically. Quattro allowed Audi to dominate rallying for nearly a decade in the 1980s, but heaven help you and your bank account if it went wrong.

These days, computers are involved in most AWD systems. Sensors on each wheel monitor traction, wheel speed, and several other data points hundreds of times a second. An ECU (engine control unit) dictates where power is sent and to which individual wheel depending on whichever has the most grip.

This type of system, usually called torque vectoring, appears on everything from the Subaru WRX to the Dodge Charger these days. Torque vectoring has allowed massive improvements in handling and all-weather capability.

AWD ProsAWD Cons
Provides increased grip and control under all road conditionsReduces Fuel Economy
Gives sportier handling and traction to a broader range of carsIncreases the weight and complexity of vehicles
Works all the timeNot as good in extreme off-road conditions


As the pros and cons show, your four-wheel drive system decision depends on what you need the system for. Again, I’ll bring up that Crossover vs. SUV debate, because it probably addresses the two types of vehicles you’re shopping right now.

If you plan on using your vehicle off-road often, 4WD is definitely the best bet. 4WD appears on pickups and truck-platform SUVs that have the durability to match the ruggedness of a 4WD system. For most people, however, AWD makes more sense.

In the sort of winter road conditions that most drivers experience, it’s nice to have a drivetrain, like a modern AWD system, that responds instantly without the driver having to toggle any switches. In addition, most vehicles featuring AWD tend to have better weight distribution, which also aids in traction (and performance).

The reality is that for many drivers, you don’t need either. If you live in an area that doesn’t get real wintery weather, you probably would only notice the difference a couple of times a year, and in many cases, your best bet is a good set of winter tires. Seriously. Tires can do far more than AWD or 4WD on all-season or summer rubber.

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