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Scoot

AWD vs. 4WD

33 posts in this topic

Can somebody explain the difference between all wheel drive and 4 wheel drive in language that a total mechanical (Contact Us Please) (i.e., me) can understand? I've asked this question to a half dozen people and gotten a half dozen different answers that don't make much sense to me.

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WEll, unless I miss my guess, it should work like this. AWD is All Wheel Drive and means ALL wheels are driving ALL the time. Four-wheel drive means the vehicle CAN operate with all wheels driving but only when YOU select ALL wheels to drive. In both cases you end up with ALL wheel drive, but with four-wheel drive you are able to selectively use the additional driving wheels. With all wheel drive you generally get modestly lower miles-per-gallon and a simpler system. With four-wheel drive you get modestly higher mpg and a more comples (but perhaps more stout) system. I don't want to get any more complex than that, i.e. discussing drive shafts, differentials etc. so as not to make it more confusing for you than it needs to be.

I'll let one of these other guys do that for (to) you. grin.gif

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All wheel drive, The drive trains are not locked, they are limited slip so you can drive on any type of surface safely without tearing up the drive trains. Anytime you turn, the inside wheels have fewer revolutions then the outside wheels. The drive train allows for that in AWD.

There is power going to the front and back axels.

4wd, Same as above but the wheel hubs get locked so there is power going to all wheels. In 4WD the drive train does not compensate for your tires to be allowed to turn at different revolutions if you are turning.

That is why your tires chirp or it's harder to turn on dry pavement.

It's ok to pull out a boat or any other task on dry pavement as long as you go straight.

Use 4WD in loose gravel,mud,ice,snow only.

Hope this helps.

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I had AWD on a previous truck and loved it. Just step on it and go, no matter what the road cond. With my F-150 now I really, really wish I had the AWD again. Really easy to get in trouble now on slick roads, because I have to think about it, then shift into 4. I have a tendacy to wait to long.

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like others have said AWD you are always in 4 wheel drive and with 4WD you have the option of being 4 wheel drive or not. With 4WD you get the option of 4 low or 4 high and it does really apply power to both axles, will AWD you normally only 4 high and there is a differietial in the transfer case so it doesn't always apply power to both axles evenly. If you are buying a SUV that is not going see any off pavement use go with the AWD if you are planning some off road excursions get the 4WD drive it is made for it.

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Alot of SUV's are full time AWD like my Explorer. I can switch it to 4WD high or low when needed.

I love the all wheel drive also.

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Depends on the brand. Basically, AWD has a center differential instead of a transfer case. There's always 1 front wheel and 1 rear wheel driving. Some Chrysler mini-vans have had the center differential explode if the front tires don't wear EXACTLY the same as the rear. With 4WD, you drive with the rear wheels providing the power until you want the front to help. Now, throw in Auto-4WD to confuse things!!!

TC

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Don't confuse full time 4WD with AWD. You have full time 4 wheel drive on your vehicle. And there are a few that have the automatic 4 wheel drive, Jeep is one I know of for sure. I am not fond of the full time 4 wheel drive mainly cuz it really drops you MPG push those front axles all the time, that and the extra wear and tear on the axles, u-joints and tires.

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I have an Astro van that is AWD. I still have a transfer case and front and real axles. It has it's ups and downs. I can get though the snow, light mud and climb hills ok. But I don't get the MPG's I'd like. It rides and look nice. I love it. I haven't had any problems with the drive line and the van is a 1999 with 150k on it. Nothing leaks or makes noise.

I looked for 9 months to find this van. Evey one I looked at some thing leaking or it made lots of noise from the front end. If you thinking of getting a used AWD look around and have it looked at by a pro before you buy it.

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Hey Scoot! Now go back and read the last line of my first post! Ha! grin.gif

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I agree that the only difference is that AWD and 4WD is the ability to decide when to engage. Auto 4WD means the vehicle is allowed to decide when to engage the front axle(s). That is why they provide the Auto/4WD selector. With it in auto the front drive engages as needed but when in 4WD position, the front drive is engaged full time.

One thing to mention. Some seem to believe that in 4WD all four wheels are driving. They are to a point. It is rare, and in fact I think it would have to be special ordered, to have a locked front or rear differential. It can be special ordered to have manual differential locks also but except for those special vehicles, our vehicles all have a limited slip differential which means that one wheel may not be driving under certain conditions.

Bob

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Ufatz are you saying we got sucked into this? shocked.gif

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Ufatz, it's like you're a prophet or something... grin.gif

Thanks for all the info, fellas. One final, related question- are there major pros and cons related to 4WD and AWD and towing? I've got an 18 foot Skeeter that's a fairly heavy boat that I'll be lugging around. Is one obviously better or worse for this purpose? Given the previous responses, I'd assume that I'll be just fine with either option.

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More than likely you will not notice a difference in how an AWD drives other than the extra traction is already there when you need it.

Personnally I don't think its necessary to have all for wheels turning at the same time all the time. I like choosing when I need the extra traction.

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I have to put my input on this.

AWD is a 4wd system with a viscous couple between front and rear drive, the vehicle always runs in 2wd (mostly front, some rear) and it gets engaged into 4wd when there is a difference of rotation, even with same axle, it is immediate and you won't feel anything just added traction, and it's a continuous operation. It's usually used on light vehicles.

4wd is the classic transfer case manual engagement or electric from dash, traction is always on 1 axle (usually rear) until power is needed on other axle. Modern trucks have a lockup to engage front axle instead of using old style manual hubs (where you get off the truck and twist the knob in the middle of wheel), this method is used on heavier vehicles, and also industrial applications.

Both systems substantially are almost identical, except 4wd has an actual transfer case with low range, possibility of PTO.

AWD is also very common on cars (Audi Quattro were pioneers in this system, now used by many mfg.), some newest version have computerized capability to have each wheel and axle spin at a different ratio to achieve total traction on any surface.

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Scoot: I rest my case! Ha! grin.gif

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I pull an 1800 Fisherman with a Ford Expedition that has AWD and 4WD. No problems at all. The only difference I ever notice is that in winter when you spin the wheels a bit AWD kicks in. It also has settings for 4WD high and 4WD low.

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Valv, hit it perfectly. AWD is 2wd normally, but when the car senses slip, then all four wheels will spin. With 4wd the user has the choice to turn it on and off. With 4wd even when the wheels are losing traction if the user does not turn the 4wd on, it will only be 2wd.Most awd vehicles you do not have the option of turning it off and on. Just think of awd as being for people who are too lazy to turn a switch on, and 4wd as for people who like to control there traction. But as for a safety factor, awd will come one instantly when you need it and 4wd you have to switch it on.

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Valv nailed it! I'll try now in the easiest terms I know, and yes; I know there are systems that deviate from this BASIC explanation, but let the dealers do their song and dance for each of those:

AWD on lighter, non-working vehicles with no driver input on when to engage. (1) axle driving unless slip is noticed by the vehicle and the other axle is then engaged. There is also a front and rear differential on its corresponding axle deciding which wheel to turn.

4wd on heavier, working vehicles with driver control on when to engage, some with an added high and low range. (1) axle driving unless driver wants the 2nd axle to drive, too (locking the transfer case in either a hi range or a low range). Differentials are in play here, too.

There are also limited-slip and locking differentials to get both tires attached to an axle to spin. Let alone systems that also use the ABS function to limit wheel spin to specific tires, and other traction control systems that go beyond that.

All I know is that I love driving my wife's Outback in the snow when everyone else is at home! Don't forget about all-season tires to help out too.

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Quote:

Scoot: I rest my case! Ha!
grin.gif


Ok, to make you happy here's the answer for the Mechanically Challenged (no offense Scoot).

Only difference between the 2 is:

AWD is automatic 4x4 and 4WD is push button/pull lever 4x4

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My Astro doesn't work like that. One front tire has power and one rear tire has power all the time. When they start to slip then all 4 wheels get power. The newer AWD cars work like what Valv says.

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Simply put, AWD is for yuppies and poeple that can't drive when the roads get slippery and 4wd is for people that go off road to hunt or fish.

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I was gonna stay out of this but there seems to be a lot of misconceptions about how each system works. I dont know if this will clear things up or make them more confusing but here goes. They are actually quite different systems. Here are some diagrams to help explain. In a low traction situation, with an AWD system a vehicle can theoretically spin just one tire because of the differential effect between the front and rear drive axles and the differential effect of the individual axles themselves. As long as all the wheels have traction the drive will go to all of them, but there is no way to mechanically lock the front and rear together.

differential-awd.gif

On a 4wd system there is a transfer case instead of a differential between the front and rear drive axles. Because of this, there is a direct mechanical link between front and rear drive axles. This means at least one front and one rear would have to spin in a low traction situation.

four-wheel-drive-intro.jpg

On a 4wd vehicle with auto AWD the transfer case acts as a differential would unless you switch it to 4wd, at which time it mechanically locks the front and rear together like a standard transfer case would. Add a locking or limited slip front and/or rear differentials and you can make the torque turn even more wheels. smirk.gif Hopefully this clears up any questions anyone still had.

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Yeee haaaaa. Got it now Scoot?! Lovin it....just lovin it. grin.gif

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(mac's first pic)

http://i34.photobucket.com/albums/d137/macgyver55/differential-awd.gif

I gotta ask mac; in an AWD scenario, how would the "center differential" know if there is still power applied to a front tire after it is engaged? There is a front diff and a shaft going out to the center diff; If there was noticed slip in the front tires, it's my understanding that it just engages the center diff, but doesn't stop the front differential from giving power to a front tire. In order to keep just one tire of 4 driven tires turning you would need a lot of extra (and unnecessary?) guts or a system like a 4WD has.

Or is it as simple as the front diff either drives the front left, front right, or the shaft going to the rear? In that scenario, you could eliminate the center diff altogether. Thanks, I'm learning alot too.

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