*REALLY * stupid question

[2001sc2]

what's the difference between AWD and 4WD? I know there is something different among them... but wouldn't having FOUR driving wheels be driving ALL of them?
~Jim

[93KidCar]

*the only stupid question is the one that isn't asked* (somebody famous said it but I can't remember who, sorry)

Mostly the difference is from the marketing departments... of Subaru and Audi by the way... as a way to differentiate the more sophisticated "car" systems from the "truck" configurations.

4WD generally means a system that is part-time, meaning that the driven wheels "normally" number 2 but the system can be switched "into 4WD" as desired, often only on non-paved (or slick) surfaces. This change of mode used to mean stopping, moving a lever on the floor, perhaps getting out to switch a knob on the front hubs, etc. For the past 10 years or so, these part time systems, which are mostly on trucks/SUV's have been activated via pushbuttons on the dashboard so they are much easier to use. Normally, they lack a center differential to allow the front & rear wheels to turn at different speeds, so making turns on non-slick surfaces causes the whole driveline to fight itself, preventing full-time use of the system.

AWD is commonly used to badge systems that are always capable of applying drive torque to any or all of the 4 wheels and often include some system which allows the drivetrain to "decide for itself" where to send the most energy. Audi & Subaru, using quite different systems, are the mainstream "old timers" in the AWD world. Neither was the first (I think that a British company named Ferguson might claim that, who knows...) though arguably both have done the most to popularize the benefits. Currently, there are many many variations on the theme and most of the cute-utes like the VUE have AWD, which is the most suitable for the type of use these vehicles will see. The more rugged "4WD" systems still have a place in the market, though.

Hope this helps, KRK:flag:

[Russ Bellinis]

Actually the difference depends on who is using the term. The Saturn Vue is available with either fwd (front wheel drive), or awd
(all wheel drive.) The base 4 cylinder model is available with either front wheel drive only or all wheel drive. With fwd, it is more of a tall station wagon than an SUV, but from the comments that I've read on this board the awd Vue isn't really a serious off road vehicle anyway. The awd version is probably a good snow vehicle, but I'll never test anything in the snow unless I go up into the mountains from here.

[sc2_94]

93kidcar:
Then what is the difference between 2by4 and 4by4 in vehicle drive terms?
I had a toyota 4by4 once and it had the front manual locking hubs and the floor lever to change from 2high to 4low to 4high.

[Case93sc2]

I absolutely love the site www.howstuffworks.com It has a great section in automotive on 4wd and AWD.

2high is your standard rear wheel drive. 2x4

4Hi on your toyota would give you the standard part-time 4wd. 4x4

4Low would give you a different set of lower gears. It is effective because it gives you maximum engine power while turning the wheels slowly. I think in my jeep I have only used this once.

[Qlara]

How Stuff Works? Great site.....

The real definition of AWD is already blurred by some manufacturers. The closest example is VUE AWD vs Subaru AWD.....obviously they're both badged as AWD vehicles but mechanically they are performing differently..... :yes:

[Phil]

I do feel the need to point one thing out:

AWD/4WD (whichever is applicable to a given vehicle) is only used to get the vehicle moving. People often buy vehicles with these drive system for foul weather driving, and it does indeed help you get moving in the nasty stuff. Problem is, that extra drivetrain increases the overall weight of the vehicle by several hundred pounds. That added weight must then be stopped (so these vehicles generally have longer stopping distances), turned (yup- handling usually isn't as good), and moved (lower mileage). So, although you can get moving better, doing anything while you are moving is not as simple as a 2WD system.

For foul weather, unless it gets REALLY ugly, I would probably just recommend some good snow tires.

I know this wasn't what you asked, but hey, while on the topic...
:D

[Qlara]

That's right, I always have an impression that the public is kinda misleading or misunderstand the true purpose of AWD/4WD system. It does help you to take off on snow-belt much easier but it won't do magic on slippery cornering and stopping.

AWD, FWD or RWD cars still have the same 4 friction points on all corners anyway. When there's no friction on the contact pads (aka Tires), you skid with momentums no matter what. :dazed:

[BobL]

So true.

Many years ago, was driving a a CJ-5 Jeep (real Willys Jeep) on snow/ice with 4wd in low and chains on all 4 wheels.

Still skidded into a snowbank but the Jeep pulled itself out and kept on truckin'.

Ah, back when Jeeps were Jeeps not gussied up yuppiemobiles.

Totally bulletproof flathead 4.

[beasjd]

AWD will help you corner on slippery surfaces. While it is true that you have the same 4 friction points there are other factors at work. What do you do when you start to skid on ice/water/oil or whatever else? Turn into the skid is the first thing most people would say. But there's more to it than that. You should also be easing down on the gas pedal. That way when one of your drive wheels catches a bit of road or rough ice where it can get traction it will "pull" you out of the skid. Here's where AWD helps. By having 2 extra drive wheels, you stand a better chance of one of the drive wheels getting traction and helping to pull you out of the skid.

[Spanky]

:hmpf: I'll have to disagree with you there, beasjd. Power to all four wheels will help you get moving or unstuck, but power to the rear wheels will not help you out of a skid, in fact it might make it worse. That is unless you have four wheel steering. There are two things that will help get you out of a skid. 1) pulling at the front wheels, to force the front of the car in the direction you want to go faster than the rear is sliding in the direction you don't, or 2) or a normal (perpendicular) force at the rear tires, such as a dry patch of pavement or curb, which will stop the back from coming around. Traction force from the engine (parallel force) will only move the vehicle forward, and if the wheels that steer aren't getting traction this won't stop a skid.

I do agree that easing off the gas or break is the proper way to recover from a skid. I was lucky enough to get to take an advanced driving course. In one exercise the instructor had a button he could push to momentarily lock the rear wheels and force the vehicle into a skid, then we would attempt to recover. It's a lot of fun when it's someone elses car and there's nothing to hit. :D

[2001sc2]

Yes, but in a slide, I hope you're not using your drivetrain to save you. Otherwise, please don't ask me to be a passenger in your car. The following is intended for RWD, but this same technique is effective for FWD too.

"The first reaction is with the hands - dial in opposite lock, steering in the direction that the rear end of the car is trying to go. This is the "correction" phase of skid recovery.
The second, almost simultaneous action should be to settle the rear of the car by transferring weight onto the rear tires. You do this with throttle application - a little throttle application. A common mistake here would have been to instinctively jump on the power to save the slide. If you did that, you would have lost cornering traction at the rear by asking for too much accelerating traction"

Also, if you yaw out more than 90 degrees, you're toast so the golden rule is "if you spin, both feet in"
"If you lock up all four tires they'll lose all their cornering ability and the car will continue on in a straight line... If you don't lock the brakes, the car could do one and a half rotations, catch cornering traction, and dart back across... into the path of other cars..."

info borrowed from
"Going Faster! Mastering the Art of Race Driving"
The Skip Barber Racing School Textbook

[beasjd]

Originally posted by 2001sc2
Yes, but in a slide, I hope you're not using your drivetrain to save you. Otherwise, please don't ask me to be a passenger in your car. The following is intended for RWD, but this same technique is effective for FWD too.

"The first reaction is with the hands - dial in opposite lock, steering in the direction that the rear end of the car is trying to go. This is the "correction" phase of skid recovery.
The second, almost simultaneous action should be to settle the rear of the car by transferring weight onto the rear tires. You do this with throttle application - a little throttle application. A common mistake here would have been to instinctively jump on the power to save the slide. If you did that, you would have lost cornering traction at the rear by asking for too much accelerating traction"


That's using the drivetrain to save you. You're easing on the gas to get the car to "pull" you out of the skid. That's the exact same thing that I said. Most peoples reaction would be to slam on the brakes. Brakes make your car stop, so if you slam on them, your car will stop right (sarcasm)??? :dizzy:

And if you can get the back wheel traction, it'll at least help you to stop skidding by putting you in a straight line, instead of spinning. If it doesn't improve handling why do almost all rally cars use AWD?

[Phil]

Originally posted by beasjd


If it doesn't improve handling why do almost all rally cars use AWD?

If you notice, most rally cars use the "point and claw" method to change direction at high speed on a rally course. This method is wholly unsuitable to "normal" driving (not to mention the far superior skills of the rally drivers- those people are good). AWD tends to make "normal" handling a bit more predictable (through understeer). However, where traction is hard to find (snow, ice), the extra weight becomes a liability when turning. What you can do on a dry road means nothing when the tires simply aren't hooking up. The little traction that can be found in an understeering skid in winter will have greater effect of a FWD or RWD car, because of the lighter weight.

I am not knocking AWD at all- I wouldn't mind a Subaru. The problem comes when people think that 4 drive wheels negate basic laws of physics. :fish:

[Qlara]

Yup! That's the point I hope the public can understand toward AWD, 4Motions, Quattro blah blah really can/can't do.....

It's so true 4-wheel drivetrain will help you take off faster in snow. However; when Zero-friction applies to the equation of skid factors, no drivetrain will make a difference since what holding up the car are the same 4 tires......well, 4 x 0 = 0 anyway.

That's where a set of good Snow tires come into rescue..... ;)

[ViPeR_PsY]

or you could screw tires and buy an M1 Abrams off the black market :cool:

[Saturnmeister]

I think the AWD/4WD line isn't so clear as has been represented above regarding "part time" vs. "full time", because there ARE "Full Time 4WD" systems - see Jeep for good examples of these. Rather, the dividing line would seem to be more one of systems designed for serious off-road use, generally with 2-Speed Transfer Cases, and those designed for on-road or rough road use, which are the AWD systems. I know I've got some detailed write up in some magazine about what the differences are, but technical detail aside, that's the real difference - 4WD (particularly with a 2 Spd Transfer Case) is made for serious off-road duty, AWD is not.

Now if you want to talk about the stupidity of people who think that AWD/4WD = "I can go as fast as I want under slippery conditions", I'll join the rant. In particular, I hate the new VW ad for the Passat "4-Motion", which REINFORCES the stupidity by suggesting that someone sliding around out of control would be assisted in ANY MANNER by having an AWD Passat - in point of fact the AWD Passat would be WORSE off, becuase it has the extra weight - and is therefore that much HARDER to stop once traction is lost :x . The fact that the number of driven wheels means NOTHING (good) once you're trying to slow/stop, and that in fact such vehicles take LONGER to stop - needs to be POUNDED into people's heads!!! :redjump: