AWD vs 4WD?

I guess that car shoppers just need to be aware that vehicles that let you shift into 4WD drive usually cannot be driven on dry pavement for any distance in 4WD mode (tires will chatter like crazy in turns and it is very stressful for the vehicle in general). This used to be a big deal when you had to get out and lock the hubs for 4WD, not so much so with the modern shift on the fly systems. I believe that PhilT is referring to these as part time 4WD drive, but I've also heard people use that term to describe systems that automatically shift power away from the front wheels to the rear when needed.
PhilT is absolutely correct about the terms getting very blurry here...Toyota calls the system on my RAV4 4WD, but it seems to be similar in operation to the AWD that my Outback had (which seemed to work better). I do like the button that pops it into electronically locked 4WD, but it's a shame that it kicks itself out of that mode at 25mph...a 35 or even 30 mph threshold would make it a lot more useful.

No, not quite like that.  That shows drifting with lots of traction available, lots of fun (and expensive) to be sure, but I meant more of a low-traction situation like rain on top of freezing rain with the crucial bit being the transition from not drifting to drifting. 

 Go on and believe what you want. As someone who has been driving AWD cars for about 25 years, I'll just say that hasn't been my experience.

I used to see lots of 4WD sport utility vehicles off the side of I-93 on days when the highway was snowpacked. They had seemingly just driven straight off the road. 4WD vehicles whose systems are not designed to be driven at highway speeds as AWD behave oddly at speed when in 4WD mode , sometimes exhibiting strange steering behavior. Even at slow speeds on dry pavement these vehicles exhibit their peculiarities. I've even read comments by off roaders who wished their vehicles had some kind of proportional 4WD system similar to AWD. On slickrock at slow speeds the inside front tire can hop and chatter as someone mentioned thus losing traction.  You can imagine the effect of this kind of thing at highway speed on snow. There are good reasons why many manufacturers manuals warn against driving in 4WD above low speeds.

One trick to getting up and over a slick hill with any vehicle that has traction control is to simply turn it off. Counter-intuitive, but time and time again I get folks up my steep driveway in the White Mountains by telling them to do this - and most don't even know how to, or that there is an on/off switch.

It turns out that most traction control systems apply the brakes to any spinning wheel which eventually causes you to lose momentum and stop right at the critical point, or kicker, you're trying to get past. Then you have to back down and try again and again until you finally flick the switch off and breeze over it the first attempt.

The traction control works fine I guess to possibly stop a spin-out from an overly clumsey move (like entering a slick roadway with the throttle floored - I only know this from experimentation on open roads trying to figure out what the heck the traction control is good for), but IME having simple car control skills, understanding how to maintain momentum, and always striving for smoothness on all steering, braking, and throttle inputs are what really counts. Tires are the next most important thing, and then the third most important thing would be the drive system.

Chris and olsin, Ford,Mercury,Lincoln traction control has clutches to reduce power to spinning wheel, doesn't apply brake to spinning wheel, same for chrysler products. Thats why for best gas milage on dry pavement you turn off traction control for these vehicles. I'm not sure what system GM or other manufactures use, I've only owned a lincoln with traction control, but am currently evaluating a Chrysler for purchase.
My Dodge Ram 4x4 is AWD with 4WD and LSD on both diff'ls, it has a 545rfe transmission and NP243D w/elect switch transfer case. No problem switching from AWD to 4WD on the fly, but be careful where, on snow covered highways, don't switch on the curves it really wants to go straight when 4WD locks in.

 but be careful where, on snow covered highways, don't switch on the curves it really wants to go straight when 4WD locks in.
So true. You can run 1 locker and the other disengauged on corners with some control,when climbing hills. However, on the flats just kick them out and run the power-divider through the corners.

 

 

When I was test driving an Outback some years ago, the salesman told me that a batch of them with a new super fancy traction control system were delivered to an icy lot, and they couldn't get the cars to move an inch. In a situation with little traction for all the wheels, the system's response was to provide no power to any wheel.
Could have been an urban myth, but it was strange to hear from from a Subie salesman. He did say that the cars got a quick software update to improve the situation (I think these were the VDC Outbacks).
I didn't buy a car, but not because of the traction control...they had shrunk the cabin and the driver's position was no longer comfortable to me, whereas my '96 Outback was like sitting on a sofa in my family room. I worked with 3 guys who were also 6'2" or taller and we were all Outback drivers, but they lost all of us with the new vehicle. I am just barely comfortable in my RAV4, but the Outback was just not workable anymore.

I'm not sure that the difference in technology between manufacturers to slow down the spinning wheel, whether it's using a clutch to disengage power to reduce spinning, or brakes to reduce spinning by friction, really matters as they all have the same end result - which is to artificially impede the momentum that you need to get over the steep kicker on my driveway (and other mountain roads). Sometimes you just need to have a moderate amount of momentary spinning take place on the slickest spot as your momentum will carry you past that spot to where you can usually regain some traction in a spot a few inches or feet ahead - and sometimes it's just one wheel at a time using the momentum to carry you forward. Like ABS, these artificial inputs are far from momentary, due to having to the manufacturer having to engineer timing parameters for typical utilization, etc. into the system. 

We've used this trick successfully with dozens of different vehicles, typically to the amazement of the vehicle's driver.

All I can say is that if you do have a "traction control" button (or other name like "vehicle stability", etc.) and you can't make it up with the button turned on, then give it a shot with the button turned off, and you'll hopefully make it.

Quote first from first paragraph;
I'm not sure that the difference in technology between manufacturers to slow down the spinning wheel, whether it's using a clutch to disengage power to reduce spinning, or brakes to reduce spinning by friction,

Clutches reduce the applied torque to the faster turning wheel, and increase the torque to the slower turning wheel. I'm not sure on how the brake systems work for increasing traction. With the clutch system found on the Lincoln and I believe on the Chrysler, one wheel is not totally prevented from spinning, but both wheels spin at the same time, much like a LSD.
Also the difference on my Dodge Ram in AWD is 48% to 52% torque frt to back, and in 4WD it's 50% to 50% torque frt to back, when drive wheels are locked together steering is effected (you can still steer) just a very noticable difference. But the increase in traction is alot.


Quote first from last paragraph;
All I can say is that if you do have a "traction control" button (or other name like "vehicle stability", etc.) and you can't make it up with the button turned on, then give it a shot with the button turned off, and you'll hopefully make it.

"Traction Control" and "Vehicle Stability" are two different things one system effecting traction overcoming differential design and other system effecting steering overcoming roll and yaw.

You can have both systems or either system independently, BTW the Vehicle Stability will be a requirement in couple of years, I think in 2011 (like Air Bags) but Traction Control will not.

The equivalent in a RAV4 is to turn your "Lock" button on...not sure if other Toyotas have this feature.

That's not correct.  The lock button in the RAV4 puts it into a 4x4 lock mode, it locks up the differentials.  Traction control keeps your wheels from spinning on startup (which as ChrisfromRI pointed out can be detrimental in the snow).  Stability Control, as Steve2ski pointed out, is also something different, dealing with yaw control while you're moving.  I've never felt that kicking in any car I've driven, not even sure if you can feel it, but I've read that it's actually very helpful in snowy conditions.

However, the Lock button on the Rav4 is neither Traction Control nor Stability Control related.

The traction control thing happened to me in a volvo. Took a while to figure out what was going on and finally got going again after turning the silly 'snow mode' off.

It may be anecdotal, but when the spring blizzard of '03 hit the rockies and shut denver down for four days, ours was the last vehicle over Berthoud and the only one moving on I-70. Subarus, Lexuses and all other manner of AWD cars and chained up semis were stalled in the middle of the highway while our Jeep Grand Cherokee in 4X4 low went slalomed around them all the way to town.

The fact we were stupid enough to leave Winter Park at 2pm on the most epic powder day in a century only to get stuck for three days in Denver with all highways closed is another matter altogether~

On the "traction control" thread, I found that traction control works very well by keeping your wheels from spinning in snow while on level ground, moderate inclines and during turns.  I live on a hill, and when it's covered with snow, if I push the accelerator to the floor, the traction control will limit the throttle, and keep me moving at the same pace  - confidently up the hill, through the snow and around corners. Traction control, along with good quality snow tires, got me everywhere I wanted to go in my 2WD Chevy Impala - even got me around stuck 4WD vehicles!  Now, if you want to have some fun - there's a button on the dash or shift lever to turn the traction control off  - and you can do some donuts - whoo-hoo

I find that is only true when the snow's not too slippery.  If you're talking about very slippery conditions such as new snow over icy roads, or very wet slushy snow, then Traction Control will bring the car to a halt on hills.  However if you turn the TC off, and get a little wheel spin going, you can still get up (up to a point, obviously, if things get too slippery, you're not getting up with or without TC).

This may be an old thread, but it was full of useful information I didn't know as well as the information that I could have added to the discussion. Questions I've asked on other forums with few useful answers were answered in this thread.

I've had a FWD Camry with Michelin Artctic Alpins that was amazingly good, a CR-V with Nokian WR's that was even better, and now a Hyundai Tucson with lockable Borg-Warner 4WD and Nokian WR G2's that has been pretty disappointing, especially when I see Subarus (probably with just all season tires) kicking my ass in bad snowstorms. I may not be in the Rockies, but the conditions in the Adirondacks can get pretty insane from time to time.

I'm getting rid of the Hyundai before the bumper-to-bumper warranty expires and getting a Subaru Outback.

To all you 4x4 experts:

Our company has a part time Ford F150 that required some seals replaced.  It was suggested that the seals failed prematurely because of driving at "too high a speed in 4x4 mode.    Not that I know anybody that would do such a thing, but how could simply driving at 150 kph instead of 70 kph on an icy road cause the seals to leak? I can see driving in 4x4 mode on pavement putting a lot of stress on things, but how can speed damage it, other than by causing a crash of course?

To Phill:
You hit the nail on the head.  The terminology has become fuzzy. Not only is it fuzzy, most car salesmen cannot even bypass the buzz-words and  tell me what sort of differentials their cars come equipped with.  

To add to Phill's comment:
Long ago you had two choices: full-time 4 wheel drive with what was for all practical purposes an open differential between the front and rear that allowed slippage between the axles to account for different tracks of front and rear tires around a corner, but could not be switched off and a part time system that would allow little or no slippage when engaged, but sent no power to the front wheels when not engaged.  Hence the full-time, part time terminology.   Now we have a choice of several different types of torque-sensing differentials, viscous slip, three or four varieties of Torsen diffs., open diffs, lockable diffs., etc. so the terminology has gone out the window.

Lack of knowledge by the salespeople who present these vehicles to their customers goes a long way toward fostering confusion. I tried out a new Jeep Wrangler the other day. The salesman was boasting of the fact that you could shift the thing into 4WD at speeds up to 50 mph. I was a little surprised at this since I recall my owner's manual for my 98 Wrangler cautioned against driving it in 4WD above something like 30 mph. "You can drive it (the 2009 Wrangler) at 90 mph in 4WD if you want" the salesman said. I shudder to think of driving my older Jeep in 4WD very fast. The steering gets very peculiar. It would take you straight off the road if you were in 4WD at speed on a snowpacked road. Its a great offroad vehicle actually but definitely "part time 4WD". Perhaps they really have made some major modifications to the drivetrain of the newer Wranglers. The salesman acted if he hadn't a clue. He didn't have any kind of explanation  to offer at any rate. Here I am in the market for a new vehicle and the salesman has nothing credible to say to me and I still don't know if the drivetrain is substantially different.. Back in my selling days we used to refer to such people as "order takers". It does make you wonder how someone like this manages to make a living who cannot be bothered to learn anything about his product or at least come up with a good line to shuck. On the other hand maybe its unnecessary and perhaps this guy is typical.

In a Toyota Avalon the system is called "Vehicle Stability Control" and when you turn the switch off a light on the dash comes on that says "VSC OFF" - which means you can NOW make it up that hill you couldn't when it was turned on. This is not the only car I have seen which has a "Stability Control" system that has to be turned off (versus a "Traction Control" system) to use momentum to allow sufficient traction to get over a kicker. Both types of systems impede your ability to make progress up a slippery grade, whatever they want to call it.

In my real world experience, whatever the button says, when it gets turned off the car finally makes it up my driveway! What it was supposed to in theory do to help overcome clumsy driver inputs becomes absolutely immaterial when you're physically stuck in the snow and can't get going - and this darn brilliant invention is typically the inhibitor in the first place. We have gotten all sorts of car brands up the driveway by letting them try getting up for a while, pulling on our boots and walking down to tell the driver to turn the stupid thing off (Toyota, Lexus, Chrysler, Caddie, Lincoln, Saab, BMW, blablabla). The funniest part is that most drivers don't even know how to turn it off, and I have to help them do that too.

Part of the problem with these systems is not the theory of how they work, but the compromises made in implementing them - like introducing minimum time periods that they must engage for, etc. - rather than a pure system responding only for the precise time they are actually needed, only doing just enough, etc.

Having damned what may one day be a useful feature to someone, I should say that I generally prefer no intervention from the car/SUV and am a reasonably serious driver - raced RWD sports cars for years and have taken 9 racing schools, plus several defensive driving and vehicle dynamics classes, so have decent car control skills and always strive for the absolute smoothest steering, braking, and throttle inputs (since that has worked for my best lap times on the track AND getting around the roads when it's slick).

Not to be confused with IMO relatively useless Traction and Stability systems, a "Differential Lock" is a traditional manual override that locks both rear wheels so they spin together without allowing the differential to do what differentials normally do around corners - let the outside wheel spin faster than the inside wheel. This feature comes from the world of tractors and off road equipment, and has been around forever. My Massey Fergusen 4WD tractor and my 4WD Honda Pilot have this, but again it's a traditional manual override to get more traction temporarily. The tractor has a pedal to engage it, one of eight pedals, and it's temporary because the rear diff is only locked while you're pressing down hard on that pedal - soon as you lift your foot - it's off. The Pilot has a switch on the dash, but it is supposed to be used only to get you unstuck or through something bad - a temporary and huge boost in traction. Many jeeps used for rock crawling and challenging trails have had locking diff(s) added because of the huge traction boost they provide. 

I just meant that a driver would pop that button ON to get up an icy hill, just like you might turn traction control OFF on another vehicle for the same hill...basically, the lock feature is electronically making the 4WD system "dumb" and just driving all wheels the same, which is perfect for an icy hill climb. It just stinks that it only works to 25mph, but I still use it in the winter all the time.

While it's true that a lot of car guys lack any sort of product knowledge whatsoever, you should cut them some slack. Transfercases and diffs can change 4-5 times in the same model of car through out its life. Most trucks and 4wd SUV come with 3-5 gear ratios availible. And while LSDs are standard in some packages that include distinguishing features, many are on vehicles which look exactly like a similarly equiped peg-leg vehicle. Add to this constantly rotating inventory..... I'd say it's more than reasonable to expect a salesman to know what options are availible on his cars, but it is asking a little much to be able to just point at a vehicle and have all the part numbers rattled off to you

If he is able to look up in his book or computer and tell me what kind of paint it has, what fabric the seats are made of, what epa milage it gets, how many inches of knee room there is in the back seat, what the gear ratio is, then he should also be able to look up wether it has a Detroit Locker, or Torsen Type 3, or whatever, especially if he is touting its 4x4 capability.

CHRISfromRI,
Having traction control, thier gonna beat you at the track.
http://www.moretraction.com/traction.htm

It's quicker than the zipperline bump run.

Ah, got it.

I have had both awd and 4wd.  Currently I have an awd subaru and awd jeep.  I have had 4wd Blazers and Jimmy's.   Now that I have had an awd, i wouldn't go back.  I feel they preform as well as the 4wd and it is something you never had to worry about shifting into or out of.  The previous GMC products I owned had a 4wd auto option which meant it out remain in 2wd until 4wd was needed. This was a great option.  I have never heard of what you are describing but that doesn't mean much.  I could be that the mfg. recommends you only shift to 4wd at those speeds.  I have seen that.  I don't think you can go wrong with the awd unless there is a big price difference.  The best way to make either a mean winter machine is to consider some good snow tires.  We did that on our Subaru and that beast will go anywhere. Go Luck!

Ya, thanks for that, just started using an AWD and went to get the manual when I saw this to be sure I know where the button is,

I can't claim to have read most of this thread, but wante dto chime in since the original post asks about driving from Sacramento to Tahoe in snow, which is a drive I did many, many times.

I did it every time in a Nissan Maxima (front wheel drive) with all-season tires and chains, and I passed a lot of 4WD SUVs of every kind without chains that were spun out in ditches.  The portion of the drive to Tahoe that is actually snowy is relatively short; you pop the chains on and go 45-55, and you're there in one piece before you know it.

My point is just that a $30 set of chains will get you to Tahoe just as surely as a $30,000 SUV; maybe more so.  Happy skiing!

Though that is not the driving situation I find most challenging, I do think I would be happy with the WRX STI's 4x4 system 

from http://www.seriouswheels.com/cars/top-2007-Subaru-Impreza-WRX-STI-Limited.htm

"Center differential lock-up is controlled by both a mechanical limited-slip type differential and an electronically controlled limited-slip differential. The mechanical limited-slip differential activates and operates initially in response to changes in engine torque, improving overall vehicle stability when accelerating or decelerating. In automatic mode, the electronic limited-slip differential controls the differential lock-up by evaluating the amount of lock-up in the mechanical limited-slip. The total amount of lock-up is based on the combination of both differentials. A steering sensor input improves torque transfer response by more accurately relaying the car’s cornering situation."

Something very predictable about mechanical diffs.  If their electonic diff uses this as a starting point, then it's probably ok.

"In manual mode, DCCD allows the driver to select center differential lock-up to optimize All-Wheel Drive performance for varying driving conditions. The driver first selects manual mode with a console-mounted button and then turns a thumbwheel on the center console to select from among six levels of lock-up. Increasing the locking factor keeps more power at the front wheels (max. 50:50 torque split with 100 percent lock-up selected), which the driver might want in certain driving conditions or on particular road surfaces.

A helical-type limited-slip front differential and Torsen® limited-slip rear differential help to optimize power distribution side-to-side, helping to prevent the inside wheels from slipping during cornering."

I'll take a blue one.  How much is that?   Never mind; I have to put my kids through college, and a mortgage payment to make.

Edited by Ghost - 8/29/09 at 7:44am

Didn't read all the other post here.

Is the OP still reading this ?

If so, if you don't buy a Subaru Outback your wasting your money. If not a Outback, then at least a Legacy.

It really is that simple.

Here's one video some may enjoy if you like the Ken Block video.
http://videos.streetfire.net/video/IMV-Films-Gymkhana-SPOOF_694713.htm

 Click Max's link. 

Ghost - I can't help agreeing with you about the mechanical diff., but I do have to point out that F1 cars use electronic diffs.