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Comments
The two most popular configurations on non-truck-frame SUVs today are:
AWD = Automatic Wheel Drive-- one axle normally until slippage occurs. Usually no 4-lo gear
P-4WD = Permanent 4 Wheel Drive-- both axles driven all the time, with a near 50/50 torque split. Vehicles that come close to 80/20 split should really be called AWD. Usually no 4-lo gear.
Of course an exception to both examples above are Jeep Grand Cherokees which can be configured with Select-trac, Quadra-trac and Quadra-drive, all with transfer cases and 4-lo.
-mike
Think of open diffs as the easiest to get the vehicle stuck (low end of scale) and locked diffs as the hardest (high end). I'm not looking for any explanation of how LSDs work, just subjective views on how effective they are, particularly in situations where locked diffs would keep you going and LSDs would get you stuck.
I'm sure any differences would become apparent only on non-paved surfaces, so lets start there.
open/unmanaged
limited-slip (viscous)
limited-slip (torsen)
open with traction control
lockable
-juice
I guess that I really consider LS diffs to be better suited to powerful road cars rather than off-road machines. I just about all cases it is my opinion that a switchable locker, like an ARB, is the best option. The open diff gives better stability than a LS on slippery highways, and the locker is always there IF you need it. The flip side is a LS making your vehicle squirrley on slippery roads and slipping uselessly itself under duress off-road.
-mike
Also came to the same conclusion that open diffs are OK on the open road with an ARB air locker switched on for the tough stuff. But since not having direct experience, I wanted input from others.
Now all I have to do is find the considerable dough to cover the locker, compressor and installation. (compressor alone is $200)
-mike
-mike
Audi uses traction control now, so that's not a problem. However, newer Miatas have torsen diffs in the rear, and one tire on ice can get you stuck.
Ironically, older Miatas had a viscous coupling, which doesn't have this set back. The torsen is better for the track, however, so that's why they swapped.
-juice
The compact Double Differential Unit serves as both the front differential and the centre differential and is located inside the four-speed automatic transaxle housing. The unique DDU uses two planetary gear sets one for the left side and one for the right side to deliver torque from the engine to the wheels. Power is delivered to the rear wheels via both a
viscous coupling and helical drive gear. In normal on-street situations, the power is delivered to the wheels by the helical gear. The viscous coupling action is bypassed.
In low-traction situations, when sensors detect a difference in wheel speed between the front and rear wheels, driving power is transmitted via the viscous coupling to the wheels with better traction (those determined to be moving more slowly).
The viscous coupling consists of a series of parallel plates riding in thixatropic silicone fluid. A thixatropic fluid is one in which heat causes a reaction. Both are contained in a small welded housing. When all four wheels have similar traction (they are spinning at the same speed) the plates rotate at the same speed and the viscous coupling has no effect. However, if one wheel loses traction and starts to spin faster than the other wheels the coupling locks the front and rear wheels together, channelling more torque to the end of the vehicle (front or rear) with the most traction.
Noise and vibration have been kept to a minimum by using a single serpentine belt system with an auto tensioning mechanism. The Santa Fes plastic engine cover also helps reduces engine noise.
I guess the traction control manages each differential (side-to-side).
-juice
In other words, it's fine for the light duty owners require from it, and helps in snow and ice the rest of the time.
-juice
Maybe I need to buy some steel plate and make one myself.
I will try to be simple. The designation 4wd or AWD simply denotes that there is traction in the front and rear axles, they both mean the same thing, traction on both axles as opossed to 2wd or normal.
The means to accomplish 4wd or awd are many and hence the confusion, think of it as several ways to skin a cat. Each manufacturer adopts a system based on several factors, like price, complexity, user friendly, off road agresivness, fuel economy by reducing mechanical drag or friction etc.
All these systems work on dry pavement, except when you have locking differentials and you have them on the locked position.
To answer you question, all pick ups with 4wd or awd can be driven on dry pavement.
-mike
The 4wd definition would be that the vehicle must have a selectable low range. This can be part time or full time 4wd. Part time 4wd is in 2wd normally, in most cases switching to 4wd in this type of system LOCKS the front to the rear. This causes driveline "fight", making it unsuitable for dry road use. Some of the newest systems, like the GM pick-ups, can go from 2wd to full time 4wd and this is ok for dry roads. I think you can lock the center diff (a component unique to full time) invoking the aformentioned "fight".
Now there are many variations on the awd systems as well. The most common is a full time awd like the Audi quattro system or like a modern Subaru. There are also automatic awd systems that are normally front drive and add rear traction when slippage is detected. There are several devices used in these systems. They include Torsen, Viscous couplings, and open diffs with locks. They all function a little differently but produce the same end result of dividing torque amongst four wheels. If it says awd, it IS safe for dry roads.
What is your specific model? There are a number of people here who could help explain just how it works.
OOps I guess you got my $.02 anyway.
There is no vehicle that states, do not drive on dry pavement.
I remember at Edmunds Live they had a Durango, and we're talking about a quick test drive here. So people would put it in 4WD for the dirt hill and then forget to put it back in 2WD for the dry portion.
So eventually they just told people not to use 4WD for that event.
It can happen - valets, friend/relative borrows it, who knows!
-juice
SUVs on the other hand have a few choices w/low range + full-time 4wd/4wd systems that can be engaged in dry conditions.
-mike
Hope this helps!
Drew
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Vans, SUVs, and Aftermarket & Accessories message boards
-mike
Although I still prefer permanent AWD/4WD equipped vehicles, I will say that AutoTrac performs okayl. There was a demo a couple of years back where they had a Chevy Silverado pickup accelerate on a piece of soapy vinyl while in auto mode. The system transfered power to the front a brief hesitation after the rear wheels spun. Yes, it's a reactive system that cannot help all of the time, but it sure is better than a part-time only system. Of course if I had my choice, I'd go for the GMC C3 truck with the permanent AWD system :-)
Drew
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Vans, SUVs, and Aftermarket & Accessories message boards
I've got to pick the upgrades carefully since I'm not planning to do much off roading (and don't want the wife on my case). Mostly getting in and out of my own property. The AT tread tires would be too aggressive for 99% of my driving.
What's the detail on "no metal hooks" on the tow strap? They crack or something?
-mike
It's a 4 door crew-cab with a small bed, but it's car-based so probably meant for light duty (which should be OK for a construction site).
They are supposedly working on a 2.5l turbo, so it would have more than 200hp, full time AWD, and about 8" clearance.
-juice
The metal tow hooks or a chain are dangerous tools for vehicle recovery. You have it right, they break and send parts flying, not a good deal. Chain is definately the worst choice. Good forged hooks would be OK but most come with cast ones that crack easily.
-mike
-juice
-mike
Do these systems reduce acceleration? Are they only applicable at low speeds?
Thanks
Nick
From what I can find it allows you to have a 48/52 split and use it on dry surfaces but I don't know if that is locked, variable, front/rear, rear/front or what.
drew_ Feb 5, 2001 8:24pm
SelecTrac is a full-time 4WD system. In 4WD High Full-time mode, the torque split ratio is split at 50/50 front and rear; it's not variable, so all 4 wheels are powered and helping to provide traction at all times. You can leave the system in this mode on all surfaces (since it has an open centre differential) without any decrease in fuel economy.
CommandTrac is a part-time system and lacks a centre differential. It can only be activated on slippery surfaces such as snow/sand/mud.
Drew
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Vans, SUVs, and Aftermarket & Accessories message boards
I think the AutoTrac is 2WD Rear untill slip occurs, then it brings in some of the front wheels.
If this is true, what does SmartTrac do differently?
-mike