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AWD vs 4WD

Posted: Tue Sep 23, 2003 10:59 pm
by LaureltheQueen
I know subaru boasts about all wheel drive now, but when the b1 legacies were made, was it a 4 wheel or all wheel drivetrain. My badging says 4, but i know thats before they called it all.

For reference:
All wheel driver=all 4 wheels get power at the same time
4 wheel driver=2 wheels get power, 1 front, 1 back

Posted: Tue Sep 23, 2003 11:17 pm
by Legacy777
it's awd.....badging just said 4wd.......this was before the whole name recognition bs changed......and rather then try to explain it to everyone....they just used 4wd

Posted: Tue Sep 23, 2003 11:33 pm
by Brat4by4
You got the reference backwards. All wheel drive is like front wheel drive with a driveshaft and another open diff thrown in the back (for simplicity sake). 4 wheel drive locks all for wheels together with no open differentials anywhere. Or at least that is the way it used to be in the good ol' days. My Brat locks all 4 together regardless, you can tear up the drivetrain on dry pavement using the 4wd because there is no give. Whereas the Awd Legacy could possibly spin one back wheel and one front wheel to oblivion which is not possible with 4wd.

Now-a-days "4wd" most trucks aren't really true 4wd. They use electronically controlled diffs that are supposed to lock up in 4wd. Notice I say "supposed" to. There is no true mechanical locking of the diffs. Try explaining that to the Z71 off-road package full-size GMC Sierra truck that I had to pull free with my Brat. He was high-sided up front and all 4 tires were NOT turning... if that was the case, a light tug would have freed him. Noooo, only 1 wheel was turning! And four-wheel low was grinding and wouldn't engage either. So I have to yank him hard with my 2200 lb truck and all 95 lb/ft of torque and actually dislodge his frame from where it was touching. We took pictures, and he was pissed about that... serves him right, though. And Jeeps claim of "Full-time 4 wheel drive" is a joke, that's called all-wheel drive.

Posted: Wed Sep 24, 2003 12:49 am
by Yukonart
Hmmm. . . I'm wondering if that GMC's transfer case was shot. There should have at least been two wheels spinning. :?

Posted: Wed Sep 24, 2003 1:41 am
by ciper
It doesnt say 4wd on the back of your car. Thats a stylized A

4WD and AWD have nothing to do with how many wheels will spin.
Althouth not always accurate AWD should mean that all four wheels get power all the time while 4WD means the vehicle is primarily 2WD until you choose 4WD.

Even in the 4wd vehicle you describe with two wheels spinning, the other wheels are still getting the same amount of power. Thats how an open differential works. Each side gets equal torque, when your stuck the wheel with traction doesnt get enough power to spin.


Usually 4WD means a locking connection between the front and rear differential. If the front and rear differential is open thats where 2 wheels spinning comes from. If the rear has an LSD then you have 2.5 wheels spinning. Modified vehicles can have locking differentials in the rear and posssibly the front having 3 or 4 wheels spinning.

The problem with any locked differentials is that you cant make a turn without dragging a wheel. That is why you dont drive a 4WD truck on the street with the 4wd engauged.

If you follow the same description of "x wheels spinning" then you should realize that hondas only have ONE FRONT WHEEL spinning!

Posted: Wed Sep 24, 2003 2:09 am
by Yukonart
ciper wrote:If you follow the same description of "x wheels spinning" then you should realize that hondas only have ONE FRONT WHEEL spinning!
The problem with most Hondas (including my own) is that there's seldom enough torque to make this happen. :roll:

:D

Posted: Wed Sep 24, 2003 4:43 am
by Brat4by4
Yeah, I think we are both saying the same thing. I didn't go into LSD to keep it simple. Oversimplification I guess you could call it. But in general Awd means all 4 get power but one or more CAN spin. In true lock them up 4wd style all 4 have to spin. In driving my Brat and Legacy in really slippery conditions... I prefer lock-em up 4wd for the real nasty stuff - more predictable. There is no waiting for the Awd system to "react" or compensating for a different wheel getting power all of sudden.

Posted: Wed Sep 24, 2003 7:34 am
by eastbaysubaru
I was about to say the same thing about the AWD badging. It is indeed a stylized "A". But yeah, AWD vehicles typically can't be put in 2WD mode. 4WD vehicles can typically select 2WD or 4WD. The other explanations of locking diffs are spot on from what I've gathered.

-Brian

Posted: Wed Sep 24, 2003 1:02 pm
by 91White-T
Brat4by4 wrote:All wheel drive is like front wheel drive with a driveshaft and another open diff thrown in the back (for simplicity sake). 4 wheel drive locks all for wheels together with no open differentials anywhere.
All right, I have an open front diff and a LSD rear, now what does that make my car? 3WD?

Posted: Wed Sep 24, 2003 7:12 pm
by ciper
91White-T: If its automatic it would be 2.5 powered wheels and if manual it could be from 1.5 to 2.4

The center differential in the automatic will act like a locking unit under low traction and low speeds. This will get one front wheel and one rear wheel to get power. The LSD will transfer some of that power to the second rear wheel, so 2.5 wheels powered

If manual it depends on wether a front or rear wheel has traction. If only one front wheel has traction then the other will spin and a smaller amount of power transfers to the rear differential. If only one of those gets traction then power from the front passes through the center and also through the rear diff. This means the front wheel that is spinning free has to sping at some insane rpm just to get the rear to move.
All the discussion of people getting stuck with 5 speed WRX is from this.

Posted: Wed Sep 24, 2003 7:54 pm
by Brat4by4
I think he was just trying to be a smart a..

Posted: Wed Sep 24, 2003 8:55 pm
by 91White-T
Brat4by4 wrote:I think he was just trying to be a smart a..
Haha.. I really was :lol: