4wd vs AWD??

[pwjm]

Maybe I'm just not looking hard enough but a lot of stuff I found on google relating to how each of these systems work is a lot of marketing BS.

 

I continually hear conflicting ideas from friends and media about how awd systems work.

 

I understand 4wd systems. Both one front tire and one rear tire have power going to the tire with the least amount of traction... Limited slips and lockers fix this, and that's why people install them.

 

On most AWD cars, isn't it safe to say that unless they have at the very least, a center diff with LSD, only one tire on any given corner of the car will get the power, and it's most likely to be the tire with the least traction.

 

Am I missing something here? Who the hell would buy an AWD car with open diffs all the way around? And yet they are advertised as these very capable vehicles...

 

anyone know a good thorough guide that breaks it all down without the marketing hype?

[98obster]

the marketing hype exists mostly because manufacturers are very protective of their technology. there a several youtube videos on awd testing. it does seem that everyone is coming out with an awd model (at least in the mountain states) but they also may come with stabilitrack and traction control, so who knows how the awd systems work in them. I don't think subaru has misrepresented anything about its AWD. From the wheels that slip to the wheels that grip has always been true (as long as all 4 wheels have traction).

[frogstar7055]

http://www.youtube.com/watch?v=Z6-ERc-DfhA

[Scooby17]

http://www.youtube.com/watch?v=Z6-ERc-DfhA

"No vehicle can climb when all 4 wheels have 0 traction" Wait... What?

 

Hmmh. many people seem to be making comments thinking it's false. Interesting watch either way. especially how the honda/toyota drivetrain failed to climb a hill with no traction to the front axle. And VW totally lied. (or this could be falsified). either way, a great way to sell a subaru:banana:

 

Interesting that awd is not anywhere near the same across the board. As far as the question goes... 4x4 gets you at least 2 tires of traction and therefore I'd say it's better for climbing/offroad. Not sure about other purposes.

I know my awd legacy is much more confidence inspiring on icy corner than the 4x4 wagon but that could be personal preference.

 

Awd is also much more convenient as it's always there (hopefully). And won't lock on non-slippery surfaces. If awd comes with a center diff lock then it is 4x4 when that is activated.

[Twitch de la Brat]

OK, 4WD VS AWD

 

4WD in most vehicle applications is RWD when not in 4WD (Subaru is the

exception to the rule).

4WD has a transfer case that locks the front and rear driveshafts together so

that they must spin at the same speed.

Most older 4WD vehicles have open differentials

4WD's most generally have solid axles.

 

AWD usually is a limited slip differential or some sort of clutch pack controlling

the front to rear power transfer.

Older AWD systems used open differentials in the front and back but newer

systems use complicated limited slip differentials and clutch packages.

 

Or just watch that video :-p

 

Twitch

 

PS: FWD modified AWD systems are the most common in auto manufacturers.

Subaru is the Oddball in this case.

[GeneralDisorder]

There are so many variations that it is highly dependant on what you are looking at. As for Subaru, these are the systems:

 

1. 2WD (FWD - need I go further?)

 

2. 4WD - locked 50/50 torque split just like a truck.

 

3. Full-Time 4WD - Subaru did this in the 80's. It's AWD with open diffs all around. The 5 speed versions also had lockers in the center diff - when locked they are just plain 4WD as in #2 above. The automatic version is basically AWD (4EAT) as below.

 

4. AWD - in this scenario there is some form of traction device in the center - either an electronic clutch pack that can vary the torque split (4EAT) or a center diff with a viscous coupler (5 speed). In both cases there will always be power to the front and the rear even if you lift a wheel.

 

Now other manufacturers do many different things - but one thing you fail to observe is that with ABS systems being ubiquitous these days it's a simple thing to add "electronic traction control" to an AWD system that has simply open diffs all the way around. When a wheel slips or has no traction you just apply the brake to that wheel. Done with a computer and wheel speed sensors this system is VERY effective.

 

Also - from a performance standpoint - not just considering the "all 4 wheels on ice" scenario - even with open diffs AWD has much to offer. When you *do* have traction you now have twice as much contact patch for the same size tires. This makes starting, stoping, and handling much more responsive.

 

GD

Edited December 10, 2009 by GeneralDisorder

[edrach]

OK, 4WD VS AWD

 

Most older 4WD vehicles have open differentials

4WD's most generally have solid axles.

 

 

Twitch

 

First statement is generally true; maybe most have solid axles, but all the early EA81 4WDs don't have solid axles (unless someone modified it).

[fallenxcripple]

i own a 97 subaru and have gotten it stuck once to see how its awd works and down the highway it really is a 10/90 split it throws off my friends that it works like a rwd car when drifting but when i get stuck i have one wheel in the front and one wheel in the back spinning as much as i can tell its opposite tires sucks because now im trying to get up my drive way with one wheel because my front left axl is broke at the moment and getting out of parking lots with lips at the end are horrible also

[idosubaru]

Also - from a performance standpoint even with open diffs AWD has much to offer.

that's been my experience, the AWD definitely had advantages though i don't know the technicalities of it but the idea that "open diffs all the way around sucks" definitely doesn't play out when driving.