differences in 4WD, AWD, full time 4WD (1 Viewer)

[410225]

the main differences in Full Time 4WD, AWD, 4WD? I was looking at several different vehicles, to be specific, Subaru, Audi, BMW, Land Rover, there are so many description but the concepts seems the same. I apologize for my lack of knowledge in this field but, I just wanted to clearly understand the differences.
As I know, most of the people buy 4WD or AWD vehicle for the traction in winter driving and these days, there are so many vehicles with advanced technologies in improving tractions in severe road condition. Audi's, BMW 325,330XI, Jag X-Type, Benz 4Matic, Infiniti G35X, Subaru, and goes to the SUV category.

 

[PHAEDRUS]

OK
here goes with my understanding of the subject,
1 AWD. it will send power to the fore and aft differentials through a series of spider gears or viscous and semi viscous couplers. only one range of power ie no lower gears and no transfer case per se. just sending power to from and rear diffs. variant is with the viscous couplers wich can enable torque splitting at a specified range to the front or rears of the vehicle. ie 50/50 or as low as 80/20
2. 4wd,
vehicle with a selectable transfer case that will give you the option of only engaging the rear drive line or the front and rear drive lines. also will usually have a low range gear set in a transfer case for lower gears in 4wd mode. slight variant being twin sticks wich can send power to front or rears alone or both. these will usually not have spider or viscous couplers between front and rear drive lines and will send power to the frotn and rear at a 50/50 basis, usually no variation on torque split but not sure on this one.
3. full time 4wd.
similar to the set up of the 4wd but using a series of spider gears or a viscous coupler to enable easier on road handling of the veh. the difference between this and awd is the addition of a transfer case with an additional lower range gear set.
holy chit that was long winded but I think kind of clarifies the issue???
Dave

 

[410225]

Dave,

Thanks alot for the information. Couple of weeks ago, there was a new report in Minnesota comparing the 4wd, AWD, full time 4WD and also winter tire vs. all seasonn tires. Some of the description was not making any sense so I wanted to get some clarification on the subject. Final verdict fro them was AWD vehicle with Blizzak or comparable snow tires are the safest in winter driving(?). Did actually perform the test on a frozen lake to demonstrate all different variety of vehicle. Also did compare to rear wheel drive vehicle too.

 

[PHAEDRUS]

mn,
I think for the best handling vehicle in icy conditions I ouwld go with the subaru wagon. now before I get flamed here let me explain. the biggest problem with snow and ice driving is braking. it is a lot easier to stop a 3k vehicle than a 6k vehicle this is just simple math. remember that the full itme 4wd is basically an awd system adapted to a twin position transfer case. or the best of both worlds. as far as the safest vehicle I have worked in auto body for 4 years now and let me put it this way. if the roads are icy (not often in nw washington) the wife drives the 80.
Dave

 

[e9999]

yea, Dave, but how much skinnier are the tires on the Sube...?
that should be in the picture too!
E

 

[PHAEDRUS]

good point Eric,
point being made here that wight plays a huge factor in both traction ie more weight properly distributed will help (just on ice here) and on stopping.
Dave

 

[firetruck41]

Good explanation, that is how I understand it as well. Though there is no "standard" for the definitions, so some manufacturers pick whatever "word" sounds better for their marketing, ie. our Honda Element's system is called "Real Time 4wd", though it is a AWD type system, ~100% power to front wheels unless there is slippage, then hydraulic pressure builds and sends power to the rear differential.

 

[Riley]

>> Real Time 4wd <<

What a stupid freaking term. That marketing guy should be shot. What the hel does that supposed to mean?

 

[Scamper]

Here's a description that CR gives. I've seen other similar articles too.

http://www.consumerreports.org/main...R<>folder_id=113261&ASSORTMENT<>ast_id=333137

Tom

 

[Jim_Chow]

[quote author=Phaedrus link=board=2;threadid=13238;start=msg122172#msg122172 date=1079465192]
OK
here goes with my understanding of the subject,
2. 4wd,
vehicle with a selectable transfer case that will give you the option of only engaging the rear drive line or the front and rear drive lines. also will usually have a low range gear set in a transfer case for lower gears in 4wd mode. slight variant being twin sticks wich can send power to front or rears alone or both. these will usually not have spider or viscous couplers between front and rear drive lines and will send power to the frotn and rear at a 50/50 basis, usually no variation on torque split but not sure on this one.
[snip]
Dave
[/quote]

I don't think part-time 4wd rigs, at least Toyotas, have torque splitting in the t-case. Typically, you're either in 4wd (power going to the front driveshaft) or not. When you are, it's like driving a full time 4wd w/ locked center diff (since there is no center diff on a [part-time] 4wd rig). The 105 is still like this, right?

A buddy of mine in boston bought a Subaru AWD wagon...raves about its abililty on slick roads. In Japan (at least Hokkaido [snow country]), many vehicles including Toyota Corollas and the new Toyota Crown are AWD. I've even seen a Ford minivan in AWD. You'd be surprised at what a AWD vehicle like a subaru w/ good studded snow tires can do! FYI, most of the 4wd rigs I see there are 80's, 70's w/ front leaf springs, or Prado's w/ front leaf springs, mostly diesel since it costs 10-40 yen/liter less for fuel and gets better fuel economy.

 

[SteveLCetc]

"Torque Splitting" is a misnomer. Torque depends on resistance. How many ft-lbs of torque can you put on a nut in midair? The same amount as a tire in midair. None. Therefore, by definition, the axle with the traction is getting 100% of the torque. With a locker or limited slip, 100% of the torque is going to other tire if one's in the air (with a limited slip that's not very much, but it's all there is).

 

[IdahoDoug]

Good point Steve.

If the issue is ice performance, more weight per square inch of contact patch is a bad thing. It is the formation of water in the margin between tire and ice that makes ice truly slippery. The formation of ice is due to transitional melting from the pressure of the tire. The less the PSI, the less likely the water layer will form. We have a Sube Wagon and it's quite good on ice. But we had an Audi A6 and it was far superior. I believe it is because the Quattro system on the Audi provides a starting point of 25% torque to each of the 4 tires at all times, which minimizes opportunities to break loose. The vast majority of competing AWD systems REQUIRE slippage to activate, which means something's slipping from the get go. Want to go anywhere at any time in a car? Get a Quattro. Want to be nearly invincible, slap on a set of studs or winter specific tires.

DougM

 

[BrianDale]

I bought a 94 FZJ 80 AWD, is it possible, or practicle, to switch it to on demand 4wd, like a mile marker kit they make for the Chevys? Or is it not cost effective. I know when I switch my old blazer from full time 4wd to on damand, my gas milage was way higher. I'm new to the LC stuff.

 

[CharlieS]

Doug,

I'd agree, the Audi quattro system is a very nice setup.

Having owned a number of four wheel drive vehicles of different sorts including several subarus and audis, I'd say the quattro AWD system on the audi is the best system out there of the street vehicles I've driven. That is, for on road performance in inclement weather (I live in VT so we see a fair amount of ice and snow).

I don't own it anymore, but my favorite was an audi A4. Nice vehicle. Good ergonimics, excellent build quality, nice looking, great road manners.

Off the beaten path (not on pavement or good gravel roads) is an entirely different story and other factors come into play other than the 4wd system (ground clearance, selectability etc). I'm not sure my choice would be the same if the intended use was not good roads.

Charlie

 

[Scamper]

Brian -

AFAIK, the only way to "undo" the 4WD feature on a LC is to activate the Center Diff Lock (lock the center differential via CDL switch mod) and to remove the front drive shaft. Not exactlly an efficient means of switching. But, as I recall, those who have done so have not realized great gains in milage, so it may not be worthwhile for you.

 

[semlin]

Do a search on "part time" and "conversion" and you will learn good stuff. It can be done on a 91-92 with a kit but there is no clean conversion for a 93 onward. You can add a cdl dash switch and manual hubs and remove the front drive shaft. You will gain about 1 to 2 mpg. I believe you will also lose ABS on the brakes and the handling will take some getting used to. Robbie from Sleeoffroad did this as an experiment some time ago.

As for the different types of awd and 4wd, I am not sure what "fulltime 4wd" means as distinct from AWD but I think it means that power is more or less evenly distributed between front and rear all the time, whereas AWD is 95% to the front unless traction is lost. The distinction is a little bit hazy.
Here is an ok article on the subject directed more at cars than trucks.

http://www.difflock.com/offroad/considerations.shtml

 

[firetruck41]

I don't believe you need to remove the front driveshaft, if you do the CDL switch mod and add locking hubs, though that would be a tiny bit more fuel efficient.