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alafrontera
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4WD vrs AWD
Not sure where to ask this, not really an "off-roading" question. Figured the gearheads might read this forum 
I have two all wheel drive vehicles, a Chevy Astro van and a Suburu Impreza. I have never found a clear explaination of exactly what this means.
How does it differ from four wheel drive? Neither vehicle has a low gear range and they are permanently in AWD, you can't shift out of it.
I plan to use the van for camping and just wonder how much benefit I will get from the AWD. Also I plan to use the car for day trips or or overnights
to Ensenada and thereabouts.
I also have a 4WD Dodge Ram 1500 but really prefer to use the van or car.
low lattitude attitude
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BajaGringo
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AWD is in all wheel (4 wheel) all the time. 4 wheel drive is only in 4 wheel drive when shifted by you or the vehicle. I have both - my Yukon is 2/4
wheel drive and shifts into 4 wheel drive automatically when it senses it has lost traction in 2 wheel drive. My ML350 is AWD and gets no better gas
mileage than my big 8 cylinder GMC. With the added weight and power the Yukon has I have more faith in it to get me out of a bind than the Mercedes...
YMMV
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woody with a view
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most cars have engine power to only 1 wheel. my tundra has a limited slip rear differential so when one rear tire starts spinning the other rear tire
engages and get traction. when the 4wd button is pushed i then have 3 tires getting traction, unless the one rear starts spinning, then all 4! i could
be wrong!
AWD is what it states, all wheels all the time = crappier gas mileage.
[Edited on 11-28-2009 by woody in ob]
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bigboy
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Woody,
All open differentials apply equal torque to both wheels at all times. Go to, how stuff works, for a detailed explanation!
Just imagine if you disconnected one brake line to the driving axle and tried a panic stop. It's the same for hard acceleration.
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TMW
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As said, AWD means all four wheels are drive wheels. The differentials are not locked however. AWD does not have a low range. 4WD is usually refered
to as Part Time 4WD. It is not recommended to stay in 4WD like a long trip on pavement. When in 4WD it is harder to turn on hard pavement like
concrete etc, especially if the front has a locking differential. 4WD usually has a low range for sand and snow. Low range allows you to keep the RPMs
up and not bog down and less chance of spinning your wheels. AWD is better than 2WD for rain and snow. Because it drives all the wheels it will not
get as good gas milage as say the same vehicle in 2WD. AWD vehicles tend to be smaller or at least have smaller tires and I think that is why when
turning they do better. You find 4WD in vehicles that have larger tires especially trucks and bigger SUVs like the Tahoe.
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jack
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TW explains it all very well. A real 4 wheel drive enthusiast does not like AWD because there is no low range, but for most people they won't even
miss it. The big advantage to AWD (especially in winter) is when you go from good traction on a road to no traction, like when you hit black ice. A
part time 4WD should not be in 4WD and driven on dry pavement or damage to the system may occur. By the time you realize your on black ice it may be
too late for someone with a part time 4WD to shift into 4WD, they may already be in the ditch.
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comitan
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alafrontera
I have the Astro Van AWD and love it, it only goes into AWD when one tire slips, and contrary to belief I know that all the tires are NOT
working when stuck, I have had this Vehicle 4 years and have been everywhere in it, only stuck bad once deep,deep soft sand and high centered. One
other thing my gas mileage for the last 9,000 miles is 15.8 that includes many hours at the border and city driving. Actually the computer reads as
high as 22MPG when doing 70MPH on the freeways.
[Edited on 11-28-2009 by comitan]
Strive For The Ideal, But Deal With What\'s Real.
Every day is a new day, better than the day before.(from some song)
Lord, Keep your arm around my shoulder and your hand over my mouth.
“The sincere pursuit of truth requires you to entertain the possibility that everything you believe to be true may in fact be false”
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BajaGringo
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| Quote: | Originally posted by TW
AWD does not have a low range.
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My AWD ML350 has a low range that can be engaged electronically...
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Barry A.
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Just to confuse the issue  ---------being in 4 wheel drive on ice without studded
tires, or chains, can get you in trouble really fast as it often causes all 4 wheels to lose traction simultaneously---------zip, off the road you go.
In the Colorado Rockies we usually kept our trucks in 2-wheel drive whenever possible to prevent that from happening. The old posi-traction causes
the same phenomena, as do "lockers". Personally, I would only use any of the "switchable" systems on ice as a last resort to get you out of a bad
situation, but I admit I don't fully understand the new systems.
IF, and I really don't know, the AWD vehicle really has power to all wheels at the same time, you could be in trouble really fast on ice if you don't
have studded tires, or chains, for the reasons laid out above..
Barry
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TMW
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Barry reguarding positraction that is why GM when to a limited slip or whatever they call it, where it unlocks above 25 mph. A lot of emergency
vehicles when they hit ice on one wheel with positraction would spin out. I think most AWD vehicles apply the break to the wheel that spins. But that
may only apply to vehicles with traction control.
Anytime I drive in snow and especially ice I put the chains on. Too many close calls in the mountains. It's a long way down.
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Barry A.
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| Quote: | Originally posted by TW
Anytime I drive in snow and especially ice I put the chains on. Too many close calls in the mountains. It's a long way down. |
Yes, and if chains are installed properly, with "chain tighteners" (big rubber bands), you can drive for 100's of miles on them without ruining the
chains. In many cases, where the snow never left the roads for months (Glacier Natl. Park, MT), we left them on all the time. I once (winter of
67/68) drove on chains from Cedar City, UT to almost the Canadian border in Montana (West Glacier) (hauling a trailer) without doing much damage to
the chains---snow pack all the way! Chains work, and work well.
Barry
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Baja12valve
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I can't say too much about AWD as I don't have one. I do know that they don't have a low range, but in many instances, low range is not necessary.
Having a AWD on any dirt road would be a benefit. I ALWAYS put my truck in 4wd on dirt roads. It handles about 100% better, stops better, steers
better and takes the washboard better. A world of difference.
Open differential, the cheapest, least effective one out there. It will give equal power to both wheels until one loses traction, then it gives all
power to that wheel. Very easy to get stuck. So if you get stuck with a open diff and you stuff wood and rocks under the spinning wheel, the other
wheel may start spinning. In low traction situations like sand, snow, mud, it can be a real hassle.
Positraction. Much better. Again, power to both if equal traction, but if one starts spinning, the power transfers to the one that is not spinning.
You still have one wheel drive, just the one with the traction. With a clutch type positraction, the most common, you can arrange the clutches to
increase the torque transfer. I can jack up my truck and put blocks under the frame, lifting three wheels off the ground. The remaining one will pull
the truck off the blocks. The wheel in the air, opposite the grounded wheel will not spin. I can do this with both the front and rear. If I do a
burnout, I will put down two strips of rubber. I can't quite get all four wheels to spin on dry pavement.
Locking. Gives equal power to both wheels regardless of traction. If one is on the ground and one is in the air, both spin at the same speed with the
same amount of power and torque. The best arrangement for pure traction. Having a locker in the front can create some very bad handling manners, like
a real lack of steering. If you have one in the rear, in the rain, snow or ice, you can spin out real easily because the locker will sense one wheel
losing grip as you go around a corner, lock up the other one, now both are spinning at the same speed, bye bye. I think the new selectable e-lockers
are far better than the automatic ones.
Each differential has pluses and minuses depending on how you use 4wd and the type of terrain. I think that open differentials are worthless.
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Barry A.
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baja12valve said-------" Having a AWD on any dirt road would be a benefit. I ALWAYS put my truck in 4wd on dirt roads. It handles about 100% better,
stops better, steers better and takes the washboard better. A world of difference."
Hmmmmmm---I have not had that experience. To me the vehicle becomes much more squirrley on washboard and sandy roads when in 4-wheel drive at any
speed above about 20 mph. I NEVER put my vehicle in 4-wheel drive unless I can't progress without it. Different strokes for different
folks------
Barry
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woody with a view
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Barry
try it next time you're on a bad washboard. it SEEMS like the truck pulls itself over the washboard=smooth, instead of pounding into each rut.
[Edited on 11-29-2009 by woody in ob]
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Barry A.
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| Quote: | Originally posted by woody in ob
Barry
try it next time you're on a bad washboard. it SEEMS like the truck pulls itself over the washboard=smooth, instead of pounding into each rut.
[Edited on 11-29-2009 by woody in ob] |
Well, that would make sense under certain circumstances I suppose, such as excellerating much of the time. My conservative driving probably does not
take advantage of that factor, and maybe that explains it. Sure feels squirrley to me. I hate washboard!!!
Next time I will give er a try-------------thanks.
Barry
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Baja12valve
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| Quote: | Originally posted by woody in ob
Barry
SEEMS like the truck pulls itself over the washboard=smooth, instead of pounding into each rut.
That is what I feel. The front wheels are powered over the ruts and bumps instead of being pushed over them by the rears. I air down to 30 psi and I
don't even notice washboard roads, I can drive over them at any speed I want. I don't know what it is, but I have never been in any vehicle that
handles washboards as well as my truck. |
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ncampion
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The main difference between 4WD and AWD is that in 4WD the transfer case is used to lock the front driceshaft and the read driveshaft together thus
applying the same torque to each set of wheels. It usually incorporates a low range gear set for extra torque when necessary. There is no "slippage"
between front and rear. This gives ideal tracton when off-road or on other poor traction surfaces. It should not be used on good tracton roads (e.g.
dry pavement) as it will rapidly wear tires and cause poor gas mileage. It is also manually turned ON or OFF.
With AWD, the transfer case is always engaged, but it does not "lock" the driveshafts together, rather it uses either a viscus coupling or some kind
of open differential which allows the front wheels to turn at a different speed that the rears if necessary. The more sophisticated systems also
allow a different percentage of torque to be applied to the fronts vs. the rears. This is up to the car maker. AWD is "always on" and generally does
not incorporate a low range gearset, but may. AWD is not necessarly designed to provide traction for off roading, but as a performance and handling
feature on dry pavement. It does however provide some additional traction control on bad traction roads.
AWD is better than 2WD and 4WD is the best for serious off road use. I won't even get into the subject of differentials at this point, that's a whole
other issue.
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woody with a view
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my toyo at's say on the sidewall to run at 32??????????????????? i run em at 40 for everyday driving. last time down the beach was at 15--18 and the
tundra even pulled an F350 4 door 4x4 outta the soft stuff.
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tripledigitken
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I try to engage my "part time" four wheel drive every time it gets in the dirt, if only for a few miles, to lubricate the gears. Not engaging it
unless you really need isn't necessarily a good thing.
Ken
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Barry A.
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Ken, yes, I do that too, and for the reason you cite. Always a good idea to stir up the lubricants in the diff.. etc. when off the pavement.
I am going to try the 4-wheel drive engaged thang next time on big washboard----but I am still dubious.
Barry
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