AWD vs. 4WD

[Justin Kirkham]

Ok, perhaps a stupid post, but I was just wondering. In the early 90's, everything said 4WD, now everything says AWD. Is this just a change in the terminology, or is it an actual design difference? Also, what about an AWD firebird... :rolleyes: Probably can't be done reasonably, but has anyone else thought about this?

-DrkMind11

[nikon]

no change in terminology...AWD is something such as a subaru...or anything that is computer controlled...like a Audi Quattro....but a good ol' chev or ford truck is still considered 4wd because you still have to reach down (in lowerend models) and shift the tranny into 4wd...and lock the front wheels to the differential....chrysler made an AWD Astro van...and you know how old those things are ;)

[edge24_99]

All wheel drive spins idpentintly like limited slip kind of...4 wheel drive spins all together...

[3.4 slow to go]

pontiac made some awd 6000's.

[Tye]

AWD is always on
4WD can be changed from 2 to 4 wheel

For the most part, they are the same thing besides that. Some AWD's have LSD in front and back, some dont and the same for 4WD. Just the transfer case is different.

GM AWD:
Chevy Astrovans
GMC Syclone, Typhoon
Olds Bravada
Pontiac 6000

[Blue94V6]

Actually, AWD can be turned off, that's not the difference. AWD is also not always computer controlled, do some research on the early Audi Quattro systems. AWD is far better for performance driving because it distributes power only to the wheels that have traction. 4WD (as mentioned earlier) applies the same amount of power to all wheels regardless of the traction. An AWD f-body would be really cool, but it would also be really expensive and dificcult. As far as I know you'd need a new front axle (and maybe rear too), different driveshaft, some sort of AWD differential, and lots of time, money, and luck.


1994 Med. Quasar Blue 3.4l V6, Borg-Warner T5, Eibach Pro-Kit, KYB Gas-A-Just shocks, K&N air filter
soon to come: dual exhaust

[Josh R.]

<blockquote>quote:</font><hr>Originally posted by Blue94V6:
AWD is far better for performance driving because it distributes power only to the wheels that have traction.<hr></blockquote> What if the axles are open diffs??? Open diffs only put the power to the wheels that spins faster. Generally only computer controlled systems can be used in determing traction in AWD systems, and the same traction control system can be used in 4WD.

<blockquote>quote:</font><hr>Originally posted by Blue94V6:
4WD (as mentioned earlier) applies the same amount of power to all wheels regardless of the traction.<hr></blockquote> Wrong, only if it's a locker/LSD and believe you me you don't want a locker in the front unless you don't like turning. Actually most stock 4WDs are open diffs in both axles, which means that only one wheel on each axle is getting most of the power. If anything the rear axle in a 4WD is LSD and the front is open, which means you get 3 spinning.


So, where is the dividing line at between AWD and 4WD?? Well, I'd have to say that in the transfer case. Like in the Bravda vs the Blazer. The bravada uses a computer controlled transfer case and the blazer uses a transfer case where the driver must select. Some AWD don't have a transfer case, but we won't get into that.


check out this link:
http://www.4x4abc.com/4WD101/awd.html

[ October 19, 2002: Message edited by: Josh R. ]</p>

[Blue94V6]

<blockquote>quote:</font><hr>
Originally posted by Josh R.:
What if the axles are open diffs???
<hr></blockquote>
Full-time AWD systems have three differentials, if these were theoretically open differentials the car would be rendered immobile if traction was lost in one wheel. Therefore, you're right, but I don't think any such car exists. Actually, the comparison I was making was between AWD and FWD or RWD. AWD and 4WD literally mean the same thing, so it wouldn't make any since to compare the two. Traditionally, the difference between 4WD and AWD is that AWD is permanently or automatically engaged and 4WD is manually engaged. There are exceptions though such as the BMW 318ti which can be switched from AWD to RWD with the push of a button. The first-generation Audi Quattro's were in fact engaged by the driver (NOT by a cumputer). They used two manually engaged (from the cockpit) locking differentials. The next generation AWD's used a system known as viscous coupling (VC). VC used a silicone liquid in a casing designed so that slight speed differences were allowed between the two axles but increased slip would lead to a rapid increase in the viscosity (or, the ability of a fluid to move within itself) of the fluid which would then lock up the coupling. VC was used in two ways. Some manufacturers (Subaru, Toyota, BMW) used VC in conjunction with regular diffrentials which locked when traction was lost. Audi used VC in the center differential. This means that when traction is lost in the front wheels, the center differential starts transferring torque to the rear. Note that the former is a full-time system with auto-locking differentials while the latter is a part time auto-engaging system. This system was never put into production by Audi, but was used by several other companies. The 2nd-gen Audi's instead used a center differential that may have a familiar ring to many F-body owners. It was known as the torsen differential (TORque SENsing). Through a series a worm gears and a worm wheel, the torsen splits the amount of torque according to condition. With no slip it's 50/50, and the split changes according to the torque applied to the wheels (not according to wheelspin). Traction control and computers really do not have much to do with AWD. Manufacturers merely used a variation of ABS to brake spinning wheels. ABS pumps the brakes on the locking wheel, so essentially the traction control systems on most cars are just the opposite of this. However, newly developed stability management systems work in conjunction with AWD to increase traction. This system does not work if a driver completely lets off the accellerator in a turn. Porsche has come up with a system though that solves this problem and is probably the best AWD system to date, but it would take awhile to explain. Sorry about how long this post is, just wanted to clear some things up. I hope everyone learned something.