AWD vs. 4WD

[paddyhasneeds]

Can someone explain to me in terms a non mechanical person would understand, the pro's and con's of AWD (Subaru) vs. "everyone else" who claims to offer 4WD please?

[Defcon5]

Some VAG have a Haldex system, where it is primarily FWD, but when it detects the front wheels are slipping it progressively sends power to the back wheels

[odyssey2200]

AIUI AWD is permanent 4 wheel drive which requires 3 diff to operate without tying itself in knots

4WD is usually 2 WD with selectable 4WD and only 2 diffs

Normally 4WD can only be used on loose surfaces,

[The Game]

All you need to know is right here. http://www.youtube.com/watch?v=ooQRxlChvMw

[paddyhasneeds]

The Game said:

All you need to know is right here. http://www.youtube.com/watch?v=ooQRxlChvMw

Funnily enough I'm 3 minutes into that right now!

[cuprabob]

Defcon5 said:

Some VAG have a Haldex system, where it is primarily FWD, but when it detects the front wheels are slipping it progressively sends power to the back wheels

Yes, and also disengages drive to the rear under braking although this can be changed using angraded contoller.

Simply, 4wd drives all 4 wheels at the same time although the bias can change between front and rear.

AWD, has the ability to drive all 4 wheels but aka the haldex basd system which as previously said is FWD until the wheels slip and some drive is transferred to the rear.

[Herman Toothrot]

Isn't Haldex a viscous coupling, similar to the Porsche systems as found in the turbo and carrera 4? The slipping creates heat with causes the coupling to bind or something along those lines. Whereas the system cars like longitudinally mounted VAGS, audis etc are more permentant four wheel drive with torsen diffs?

The way an A3 Audi with the haldex system (FWD unless fronts slipping) drives compared to an A6 with Quattro (full time 4wd) is very different.

[cuprabob]

Yes, a Haldex is a viscous coupling and you are also correct that teh larger Audis use a Torsen diff which is true 4wd

Edited by cuprabob on Monday 27th December 15:45

[Hereward]

Read this:
http://rubicon-trail.com/4WD101/4WD-AWD-autoAWD.ht...

[NoelWatson]

odyssey2200 said:

4WD is usually 2 WD with selectable 4WD and only 2 diffs

You might need to split part time and full time 4WD = the latter shound have 3 diffs

[NoelWatson]

cuprabob said:

Yes, a Haldex is a viscous coupling and you are also correct that teh larger Audis use a Torsen diff which is true 4wd

Edited by cuprabob on Monday 27th December 15:45

Unless one of the axles does not have any grip

[marcosgt]

Some say All Wheel Drive some specify there are 4 wheels - Otherwise there's no difference, unless you have more or less than 4 wheels

M

[jimmy156]

marcosgt said:

Some say All Wheel Drive some specify there are 4 wheels - Otherwise there's no difference, unless you have more or less than 4 wheels

M

Thats what i thought... Just a different name for the same thing from different manufacturers, like Touring/Estase/Avant etc...

[Bricol]

Haldex is an electrically sensed difference in wheel speed front/rear, and then hydraulic pressure using a pump to cause drive to the normally non-driven wheels. Google it for a more intelligent explanation from the maker. Supposed, orginally anyway, to feel a bit funny in action.

Ferguson coupling is the viscous coupling where rotating discs slip relative to each other, warming up the fluid they are in, causing the liquid to form long chain molecules and thus cause the coupling to drive.

The integrale uses a ferguson centre and a torque biasing torsen diff in the rear, with a free diff in the front. Works well.

Bri

[collateral]

Was surprised to find that Quadra trac 2 (Jeep) is pretty much the Subaru set up, but with a low setting added. Seems to get it done

[Mars]

Semantics/marketing. If you've got 4 wheels and they're all driven they you have both 4WD and AWD.

[Scuffers]

Mars said:

Semantics/marketing. If you've got 4 wheels and they're all driven they you have both 4WD and AWD.

first sensible answer - Marketing talk.

[BriC175]

Oh god.. not another 'bi-turbo or twin turbo'esque thread!?

They're both two ways of explaining the same thing.

Edited by BriC175 on Monday 27th December 19:49

[Herman Toothrot]

BriC175 said:

Oh god.. not another 'bi-turbo or twin turbo' thread!?

They're both two ways of explaining the same thing.

Regards AWD, 4WD maybe but there are different ways to acheive AWD/4WD that are quite different technically and in performance as has already been described.

Edited by Herman Toothrot on Monday 27th December 19:51

[paddyhasneeds]

BriC175 said:

Oh god.. not another 'bi-turbo or twin turbo'esque thread!?

They're both two ways of explaining the same thing.

That's the point though, the literature and (potentially biased as done by Subaru mechanics) videos suggests they aren't.