awd vs 4wd

i thought i knew the diff, but what if an suv had

awd
4wd hi
4wd lo

??

when would one use awd as opposed to 4wd in the same car?

In general AWD means a viscous connection at the centre differential. That is a fluid coupling that allows different rotation rate between front and rear driveshafts. As the speed difference changes (ie one axle slipping) hydralic pressure in the system diverts force to the other axle. Different systems will have a different torque spit under normal conditions (ie 100/0 60/40 50/50 35/65) between front and rear. For example many AWD minivans and crossover SUVs have a 100/0 system meaning they essentially operated as a FWD until the front wheels start slipping. (Edit: these vehicles with transverse mounted motors don't really have a centre diffential per say, but the same idea applies)

Whereas 4hi and 4lo lock the centre diff.

Therefore, you should only use 4wd on surfaces where the tires can slip a little. On dry pavement a locked centre diff will cause the tires to bind when you corner tightly because of the different distances travelled between front and rear wheels.

AWD = slippery roads
4wd = off-road

4wd will act like a welded diff stopping your differential from DIFFERENTIATING the wheel speeds of the left and right wheels in a turn. It would be helpful for when you are stuck in mud/grass and once one wheel spins , then when your diff is LOCKED via 4wd mode the other wheel spins with it, hopefully giving you more traction.

AWD usually have viscous differential which uses the viscosity of fluids in the diff to control where the lock point in the wheels are depending on the torque. AWD just owns.

Basically, if you use 4WD on a regular truck on road, kiss your tranny good bye.

4wd will act like a welded diff stopping your differential from DIFFERENTIATING the wheel speeds of the left and right wheels in a turn. It would be helpful for when you are stuck in mud/grass and once one wheel spins , then when your diff is LOCKED via 4wd mode the other wheel spins with it, hopefully giving you more traction.

AWD usually have viscous differential which uses the viscosity of fluids in the diff to control where the lock point in the wheels are depending on the torque. AWD just owns.

Basically, if you use 4WD on a regular truck on road, kiss your tranny good bye.

Kinda…but not really…rarely any of the AWD or 4WD functions happen directly in the diff unless you are speaking of a Versatrac or similar system as jeff M had described… and in those system the viscosity of the fluid doesn't lock or regulate the diff locking. It is usually a set of clutches or an inertia system that will lock just the diff and doesn't really have much to do with AWD…

On most systems the slipping (differential between front and rear wheel speeds) of an AWD is taken up in the transfer case via clutch slippage. a visous coupling, or an encoder motor acting on inputs from the TCCM and a set of clutches within the transfer case…most inputs to the TCCM come from ABS wheel speed sensors that indicate when a wheel is locked or spinning…

There are so many AWD systems out there now-a-days it is hard to describe the operation of all of them in one description…

Generally _AWD allows some type of slippage within a transfer case to allow for operation on hard surfaces without excessive tire binding on corners. 4WD HI is locked in 4WD and is the same gear ratio as when driving normally in 2WD. In 4WD HI the front and rear diffs operate in unison and will bind or chirp the tires on corners on hard surfaces. 4WD LO is basically the same driving characteristics of 4WD HI but is a lower gear ratio that is performed in the transfer case usually via a planetary gear set… In all of these modes the actual diffs themselves locking (both tires on the particular diff) are independant of the AWD system… _HOWEVER some of the most modern systems (such as Versatrac) can either electrically or mechanically lock the diffs themselves when the TCCM senses very slippery conditions…

On the vehicle gerewh0re is describing you would typically use AWD most of the time. 4WD HI would be typically used when no pavement or dirt is visible and the road is completely snow covered. 4WD lo would be very seldomely used when driving off road, pulling another vehicle out of the ditch etc… 4WD LO should never be used on a road surface and only in an off road situation…

If the vehicle also has the option of 2WD it should be used as often as possible instead of AWD since in AWD you can still get clutch wear, etc.. in the transfer case as the encoder motor can still "hunt" and cause premature wear in the components. If there is only the option of AWD the system is designed for this "hunting" and no excessive wear will happen…

Hope this helps…..

4wd will kill you easier during normal driving.

Say your going into a corner, and its slippery. Hense why uve elected to use 4WD. Halfway through the corner you take your foot OFF the accelerator. Then you spin out into a tree. Thats throttle lift over steer induced by th lack of a center diff. It starts because your front and rear wheels are forced to spin at the same rate, if the speed of the vehicle and the path of the wheels doesnt warrent for this, the energy in the system is released and you will lose traction (probably in the back since youve got less weight there).

AWD has a center diff which allows all wheels to retain traction by letting each wheel spin at its apropriate wheel speed.

I prefer 4WD with an open front diff in the snow and obviously offroad driving. In all other instances, AWD is a better way to drive IMO.

http://jeep.ca/en/4X4TrailRated/

jeep knows best…

check out 4x4 basics, 4x4 systems. Freedom Drive I and II are AWD.

check out 4x4 basics, 4x4 systems. Freedom Drive I and II are AWD.

So are Select-Trac [HTML_REMOVED] Quadra Trac…..

I once watched a brand new F350 enter a McDonalds parking lot with 2" of slushy snow, put it in 4HI and proceed to drive into the covered u-shape drive thru, which was bare, wet pavement.

He would stomp on the gas until the tires would finally slip and the truck would lurch forward a couple feet. Just kept on doing that until he got his food.

Ah, Victoria.

Ive been driving around in 2wd on the roads and laughing at people who cant handle their AWD/4wd vehicles, guess people think they drive themselves.

Old toyota's are fun, you can add a second transfer case with an adapter for double low range, then a twin stick to control the hi/low function, can also add in a rear drive shaft disconnect.

with all that you would have:

2 hi
4 hi
4 low
Double 4 low
2 low
Fwd hi
Fwd low

:drool: still have the option of triple tcases converted to "crawl boxes" with lower gears, some people run dual transmissions too.. stock is good enough for me haha.

IMO jeeps have the worst 4wd systems, with exception of the brand new Rubicon's, took them long enough to figure that out.

To answer your question if a vehicle has AWD/4hi/4Low, its always putting power to all 4 wheels. The 4wd modes lock the center diff and send the power 50/50 front and rear. In AWD mode the power varies to where the computer thinks it needs the traction via the center differential and Traction control sensors. I personally dont like that type of system at all, my friends 04 Dakota has it and its blown the front differential twice since they bought it driving on dry pavement, its never been offroad and never beat on, another perk of fulltime awd is it gets about 12mpg.

marlin case adapters ftw.

But yeah…..AWD is rally the best unless you offroad and need the dependability and component strength of the 4wd. In very bad situations, AWD can drive only one wheel like a 2wd car, which is why absolute AWDs are not the best in slow technical offroad. What you're looking at is the best of both world. Being able to lock the viscous coupling in the transfer case and getting true 4wd is pretty nice. Then running AWD for daily driving is pretty convenient.

I'm pretty sure you're all wrong. AWD refers to one of these:

Because it's using all of it's wheel to drive. Yes that's it.

ATTESSA For The Win