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Is Your 4WD Vehicle Really 4WD?

Posted on December 4th, 2008 in , , | 20 Comments

Is Your 4WD Vehicle Really 4WD?
By Eric Peters, Automotive Columnist

It says “4WD” on the tailgate — and there it is again on the list of standard or optionally available equipment. But is it really four-wheel-drive? Or just all-wheel-drive pretending to be something more than it really is?

Increasingly, it’s the latter — most notably when it comes to the ever-growing ranks of  so-called “crossover” vehicles and compact SUVs. Examples of this category of vehicle include models like the Ford Escape, Volvo XC90 and Honda  Element.

These popular vehicles combine the appearance and stance (including ride height) of an SUV but handle and drive more like cars — because they are typically built around passenger vehicle platforms. They usually come with front-wheel-drive standard and some sort of all-wheel-drive system available as an extra-cost option.

But AWD is not the same thing as 4WD — and it’s arguably false advertising to lead people to believe otherwise.

Each system works differently and offers different levels of capability.

4WD used to be synonymous with a drive system in which the engine’s power is (or can be) transmitted to all four wheels through a two-speed transfer case and drive axles. The transfer case’s main function is to provide a gear reduction feature and the ability to shift the vehicle into 4WD Low range. 4WD Low range is designed for severe conditions such as pulling through heavy, unplowed snow or mud, or slowly climbing up (or inching down) a backwoods hunting trail.

An AWD system also transmits engine power to all four wheels — and will also give the vehicle a better grip on the road in inclement weather than a front-wheel-drive (or rear-wheel-drive only) vehicle. But an AWD-equipped vehicle lacks the two-speed transfer case that is the defining feature of a heavy-duty 4WD system. This means there is no 4WD Low range for deep snow/mud and uneven terrain.

And that means you should probably keep the vehicle on paved roads — no matter how much it may look like a burly SUV on the outside.

Another key difference between 4WD and the AWD systems used in many of today’s “crossovers” is that the AWD systems are heavily biased toward the front wheels.

Under normal driving, usually upwards of 90 pecent of the engine’s power goes to the ground through the front wheels — so most of the time, you are driving, in effect, a front-wheel-drive vehicle. When the front wheels begin to slip, some engine power then flows to the rear wheels via a device known as a viscous coupling. But the “default setting” in the typical AWD system is front-wheel-drive — just like the front-drive passenger cars they’re descended from.

In contrast, a 4WD system is typically based on a RWD layout and usually transmits almost 100 percent of the engine’s power to the rear wheels (the “default mode”) until and unless the setting is changed from 2WD High to 4WD High (or 4WD Low). When 4WD (High or Low) is engaged, the power split between front and rear wheels is also closer to 50-50, as opposed to the (typically) front-dominant AWD system, which usually sends most of the engine’s power to the front wheels.

These functional and design differences betray the different origins of vehicles equipped with 4WD — which are almost always descended from pick-up trucks built on rear-wheel-drive platforms — vs. the trucky looking but lighter-duty crossovers — which are almost always descended from light-duty, front-wheel-drive passenger cars.

Yet despite the clear differences in design and capability between 4WD and AWD, several automakers brazenly conflate the two as a way of bulking-up the perceived capability of their light-duty, car-based “crossovers” to make them appear less like the passenger vehicles they’re typically descended from.

But don’t be fooled.

And don’t expect a car-based crossover vehicle with a car-based AWD system to be able to do things a true 4WD-equipped vehicle would be able to do.

Comments?
www.ericpetersautos.com

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20 Responses to “Is Your 4WD Vehicle Really 4WD?”

  1. Four-wheel drive, 4WD, 4×4 ("four by four"), or AWD ("all wheel drive") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously. While many people associate the term with off-road vehicles and Sport utility vehicles, powering all four wheels provides better control in normal road cars on many surfaces, and is an important part in the sport of rallying.

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  2. Schwinn says:

    So be it… either way, it seems the 2nd gen systems both do a decent job.

  3. Jeff says:

    The 2nd Gen video shows the Selec-Trac II system, not the Quadra Drive 2 system.

  4. Schwinn says:

    Agreed, is seems the 2nd gen system works quite well, as evidenced here: http://www.youtube.com/watch?v=iJTvDDMKkqo&feature=related

    Interestingly enough, the Quadra Drive I didn’t do so well, as evidenced by this video: http://www.youtube.com/watch?v=i0bKtjvnM8Y

    Still, add one more “good” AWD system to the list (Subaru, Audi, and Jeep QD2)… any others?

    Anyone know of a list which details how much torque a system can deliver to a single wheel/axle? I did find an intersting site here which details every system out there, but it doesn’t detail EVERY system’s max-wheel-percentage in all examples. Still it’s pretty informative: http://www.awd.ee/cars.html

  5. Jeff says:

    The Jeep Quadra Drive 2 system can deliver 100% of power to a single wheel (and not deliver it to the spinning wheels).

  6. Schwinn says:

    Although my previous post was very “ad-like” for Subaru, I just realized that it doesn’t matter, as the point still stands.

    I was reminded of the validity of the test as I saw a Nissan Murano AWD stuck in his street-parking spot, while I watched his two road-side wheels (front and rear) spinning away, and the vehicle wasn’t moving at all.

    The point of the video is to show that AWD just means that some power can be delivered to all 4 wheels. However, to be really useful, the system must be able to send almost all the power away from one or two slipping wheels. The video shows that Honda, Toyota, and VW use a potentially-pointless version that can’t even take the power away from a single wheel, hence the vehicles can’t climb.

    The only other vehicle I know that has a good AWD system is Audi, which (as I have heard) can deliver up to 90% of the engine power to a single wheel – that’s probably the best you will ever see. I don’t know how Subaru’s compares to this (I would love to find out some real tests/facts) but the point remains – AWD is pointless (for adverse weather) unless you can deal with at least a single fully-slipping wheel. As shown in the video, those other vehicles simply don’t have a decent AWD system.

  7. James says:

    As an owner of a 2001 BMW x5 I must add it’s the tires that make a huge difference. I have some very capable mud and snow tires and the x5 is able to handle just about any terrain. Ground clearance is the only limitation but if it’s really rocky and very rutted you may be out further than your own skill level anyway.

    There are some really good snowboarding areas in Vermont I use and some of them are quite far from the main access road. I have seen K5 Blazers and Dodge Ram Pickups stuck because of the all season tires.

  8. Todd says:

    FWD cars can spin their front tires easily when climbing a big hill. One time I was in my car on a hill and at a complete stop. I stepped on the gas and the front wheels started to lose grip.

  9. Jeff says:

    The Jeep Grand Cherokee with Quadra Drive can go anywhere.

  10. Todd says:

    I found a video at http://www.youtube.com/watch?v=kGzpU5Chusc&watch_response

    Watch the Range Rover climb a muddy hill.

  11. Todd says:

    2009 Audi Q7 Prestige with the 4.2 V8 is a very nice suv but for some reason I like the 2009 Volkswagen Touareg 2 better. The 2009 Range Rover HSE is my most favorite suv. They all have air suspension avalible. The Touareg and Range Rover both have diff locks avalible.

  12. Fleet Admiral says:

    Audi QUATTRO=torsen. And don’t you forget it.

  13. Jeff says:

    Just don’t try to drive a true 4WD vehicle on a paved road with intermittant snow cover. You will destroy the transfer case (and maybe more) when you hit dry pavement. This is one advantage of an AWD vehicle. AWD also provides better handling on dry pavement than a RWD or a FWD vehicle.

  14. Todd says:

    The Subaru legacy is a nice car. I might consider buying that car instead of the VW Jetta.

  15. Andy says:

    A tip as it is snowing here in colorado. AWD go doesn’t mean AWD stop! And The subarus have a viscus coupling center dif. And the STi’s can lock their center dif. Technology has advanced a lot, just learn what you have

  16. Schwinn says:

    Yeah, I know it was a Subaru ad, for the most part, but it was pretty nice to see the difference between the systems. Fact is, the Subaru system isn’t so bad.

  17. George says:

    The Touareg had a 50/50 center differential with lockup clutch from day 1.

    The Touareg transfer case is what pickups should have.

    Schwinn, that video was horrible. Just overt Subaru propaganda.

  18. Todd says:

    The 2008 Volkswagen Touareg 2 offers a center locking differential.

  19. George says:

    Four wheel drive means center differential
    That is how it was done about 105 years ago.

    Pickups and Sport ‘Utes’ used to have four wheel drive until the 1970’s oil ‘crisis’, then the big 3 decided to remove the center differential. The resultant system is off-road drive. There is no center differential, you shouldn’t use this on pavement, you shouldn’t use it faster than 25mph.

    http://www.4x4abc.com/4WD101/driveline-bind.html

  20. Schwinn says:

    It should be noted that not all AWD vehicles have the same “default” distribution of power to the front wheels. Subaru AWD, for example, is more like a 50/50 distrubution “by default”. (See http://www.netcarshow.com/subaru/2008-legacy_3.0_r/ )

    So, different AWD systems have different “default” modes. But the article is correct in saying that most “regular cars” are FWD-biased. For example, a Porsche Carrera 4 has a 5/95 F%/R% default split.

    A great video on this can be seen here: http://www.youtube.com/watch?v=2OzK-oRPCbs




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