AWD vs 4WD....

[KillerCharlie]

Originally posted by: ayabe
I thought chains were illegal now pretty much everywhere because of the damage they cause to the pavement. I was in Iowa last week and I know you can't use chains there.

You don't need chains in the midwest. I lived in Minnesota and never saw a single vehicle with chains on it in my life.

In mountainous states, however, you really don't have a choice.

 

[Colt45]

Originally posted by: Savij
****I'm very likely wrong and don't mind being corrected****

I found this site very useful:

http://www.4x4abc.com/4WD101/difference_4WD_awd.html

Basically, my understanding of it is that 4WD is basically the same as a symmetric AWD system and only subaru and volvo (or was it audi) have that. Everyone else has asymmetric AWD on their cars which isn't (edit:wasn't?) as good and that's why caltrans officers make the distinction.

Audi invented it. Well... VW did. volvos use haldex.


My old quattro with a locker in the center and rear is a tank. I've never gotten stuck with it yet.



to me:

4WD is transfer case, and a low range.
2wd, 4 hi, 4 lo. With or without LSD or lockers on the front and back.
When in 4WD axles are locked to each other. "part time", not possible to be in 4hi/lo and have different axle speeds.

AWD is fulltime through open, lockers, or LS diffs. All wheels are always driven. Axles can go different speeds (no wheel scrub, not hard on drivetrain on dry pavement) unless you engage a locker on the center diff, making it like "part time" above.

Haldex and viscous coupled stuff is generally gimicky. different league. AWD lite.

 

[Jumpem]

I prefer AWD. My Forester XT and STi were exceptional in the winter.

My Frontier NISMO 4WD, was less capable. You could only really engage the 4WD on completely snow or ice covered roads. It meant in normal driving I would have to switch back and forth from 2WD to 4WD, and vice versa, as road conditions changed. And if the roads were only a little slick you were stuck in RWD, which was less than ideal.

 

[dug777]

Originally posted by: Jumpem
I prefer AWD. My Forester XT and STi were exceptional in the winter.

My Frontier NISMO 4WD, was less capable. You could only really engage the 4WD on completely snow or ice covered roads. It meant in normal driving I would have to switch back and forth from 2WD to 4WD, and vice versa, as road conditions changed. And if the roads were only a little slick you were stuck in RWD, which was less than ideal.

So ideally you'd own a vehicle that provides proper AWD, and the option of 4WD, with the option of low-range too?

Again, I'll pimp out Prados and Landcruisers 😉

 

[Jumpem]

Originally posted by: dug777
So ideally you'd own a vehicle that provides proper AWD, and the option of 4WD, with the option of low-range too?

Again, I'll pimp out Prados and Landcruisers 😉

Anything that does not require being shifted back to 2WD on dry or only marginally slippery roads.

 

[warmodder]

Originally posted by: Jumpem

Originally posted by: dug777
So ideally you'd own a vehicle that provides proper AWD, and the option of 4WD, with the option of low-range too?

Again, I'll pimp out Prados and Landcruisers 😉

Anything that does not require being shifted back to 2WD on dry or only marginally slippery roads.

My Jeep liberty ftw. RWD for dry, AWD for wet/snow, 4WD for Xtreme!

OP: The officer could be discriminating because awd vehicles are not created equal. Many suvs have no business in challenging conditions. I don't think the lexus is too often the choice of offroading enthusiasts, but I may be wrong.

 

[LordMorpheus]

Originally posted by: Zenmervolt
They are not the same thing.

4WD properly involves locking front and rear differentials and a transfer case that has a low range option.
AWD can use several methods, but it does not lock all wheels together the way that true 4WD does and will not offer the same level of traction in severe situations. However it requires less driver intervention and is overall "better" in 90% of all on-road situations because of not requiring driver action.

ZV

When you engage the 4wd on a normal transfer-case based all wheel drive system, you don't lock the diffs. the rear and front diff are open (maybe limited slip or air lockers if the vehicles is a serious off roader), but there is no differential between them - the front diff and rear diff will spin at the same speed. For this reason it is damaging to the vehicle to drive it in non-slippery conditions with 4WD engaged, in a turn the front wheels cover more ground, but if they are locked to the rear wheels, the tires must slip a small amount to make this happen, and it's extra wear on the system.

In an AWD car you have a diff in the middle connecting the front and rear diffs, so you don't have any problems driving on the road. Most AWD cars don't give you the option to switch it off. This means that it is possible for all the power to be spun out on just one wheel, with 4WD you'll have at worst two wheels spinning, with locking diffs you get all four.

Assuming open diffs, AWD will be more likely to get stuck.

Of course, most AWD vehicles on the market have some clever limited slip stuff going on in the diffs, and that changes things.