4WD vs AWD vs WHAT WHEEL DRIVE??

[V1GiLaNtE]

So I was going to post in Jake's F150 thread, but felt like I would be perpetuating the hijack. I think it would be good to capture a lot of what information was said here as a reference.

It seems a lot of folks think they understand the various nuances of "4WD", but in reality there seems to be a lot of confusion.

Let's start with the basics of 4WD vs. AWD

All-wheel Drive
As the name implies, all-wheel drive (AWD) feeds power to each corner. Depending on the system (designs vary), AWD can provide maximum forward traction during acceleration. It is especially helpful in sloppy road conditions and when driving over moderate off-road terrain. It can help get you going and keep you moving through mud, sand, and other loose surfaces. Most AWD systems deliver power primarily to one set of wheels, front or rear. When slippage is detected at one axle, power is diverted to the other axle, in hopes of finding more traction there.

Not all AWD systems are equal. Subaru’s AWD system always directs at least 20-percent of the engine’s power to the rear, and it can direct a larger amount aft if needed. Many other systems fitted to front-wheel-drive vehicles operate with 100 percent of the power normally going to the front wheels; the rear wheels then only receive power only when the front wheels start slipping.

AWD systems are especially helpful in rapidly changing conditions or when driving on a road with intermittent snow and ice. It is commonly used for car-based SUVs, as well as certain cars and minivans. (See our list of best AWD vehicles.)

Four-wheel drive
Although four-wheel drive (4WD) and AWD are designations that are often used interchangeably in advertising and sales literature, there is a difference. Generally, 4WD is optimized for severe off-road driving situations such as climbing over boulders, fording deep water, and tackling steep hills with loose, low-traction surfaces. Most 4WD systems have high and a low gear range, the latter used to increase low-speed climbing power. Some have differentials (which allow left and right wheels and front and rear axles to turn at different speeds) to be locked for maximum traction.

Modern 4WD systems are either full-time, which means they stay engaged; automatic, where the vehicle automatically switches between two- and four-wheel-drive mode; and part-time, which require the driver to manually shift between two- and four-wheel drive. Vehicles with a part-time system shouldn’t be driven on dry pavement when in 4WD mode, which could risk damage to the vehicle's drivetrain.

Now most full time 4WD system have a center locking differential. Without the differential locked you're not getting the benefit of the power distribution or "true" 4WD.

I've always admired Andrew St Pierre White's 4xOverland videos. He does a great job of describing the benefits of vehicles equipped with locking center differential in his own very PBS broadcasting way.

[youtube]EBmw6Wpfe6M[/youtube]

For vehicle equipped with these types of differential (center, locking, LSD,etc.) learn some goddamn engineering yo!

I really likes these guys simple videos. Most of these technologies are so simple and yet really cool and effective

[youtube]SOgoejxzF8c[/youtube]

Torsen Differential
[youtube]JEiSTzK-A2A[/youtube]

Limited Slip Differential (LSD)
[youtube]WeLm7wHvdxQ[/youtube]

Inner-workings
[youtube]PEdnH7_7_yc[/youtube]

[Senor_Taylor]

Now comes the question, if it has a center diff that can NOT be locked, is it 4wd? This article seems to imply that it is, and I do not agree with that.

[V1GiLaNtE]

Now comes the question, if it has a center diff that can NOT be locked, is it 4wd? This article seems to imply that it is, and I do not agree with that.

I don't think so Taylor. That sounds more like how the Subaru All-wheel drive system works. It does indeed have a center differential, but is not a selectable for locking. That I believe, is the workings of a viscous style differential where it detects slippage of the wheels and provides the power where necessary.

[D_Eclipse9916]

Now comes the question, if it has a center diff that can NOT be locked, is it 4wd? This article seems to imply that it is, and I do not agree with that.

I don't think so Taylor. That sounds more like how the Subaru All-wheel drive system works. It does indeed have a center differential, but is not a selectable for locking. That I believe, is the workings of a viscous style differential where it detects slippage of the wheels and provides the power where necessary.

Center diff can be multiple styles, not just viscous.

Taylor, 4WD and AWD are mostly marketing terms, so be careful.

Interpretation is 4wd = selectable locking transfer case or center diff. AWD = Limited Slip Center. I hope we dont get too hung up on semantics, next we will say what is a sports car or not. :lol:

[Jake]

Yeah, agreed with DJ on the terminology.

Some vehicles with a selectable, locking center diff are marked as AWD still. For example, my coworker has a Nissan Juke with AWD. But, she also has a dash button that locks it into AWD mode, versus waiting for the front wheels to start slipping. If we say that anything with a locking center diff is 4WD, her car is technically 4WD... but it doesn't have low range and won't perform as well as a "real" 4WD. My Ford Escape was the same way, but Ford sold it as "4WD"... then removed the switch for 2005 and started calling it AWD.

I like to think of it as "has low range/transfer case" = 4WD and "center differential" = AWD.

So, a somewhat related question given we are getting into semantics. With an AWD system (I'm thinking of Mom's Outback here) - it's fully automatic and the center diff manages power front-to-rear. Assuming both the front and rear diffs are open... it's very possible to get an AWD vehicle "stuck" even if one wheel has a grippy surface, because of the open diffs, right?

[rherold9]

next we will say what is a sports car or not. :lol:

Insurance considers my car a sports car so it has to be.....

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[D_Eclipse9916]

[quote="Jake"Assuming both the front and rear diffs are open... it's very possible to get an AWD vehicle "stuck" even if one wheel has a grippy surface, because of the open diffs, right?[/quote]

Yup! Shit most trucks need at least 2 grippy surfaces or somewhat grippy surfaces.

<!-- m --><a class="postlink" href="https://www.youtube.com/watch?v=qr7qEuaXeGo">https://www.youtube.com/watch?v=qr7qEuaXeGo</a><!-- m -->

Edit: FYI Video is GM promo material so pay more attention to the concept not GM plugging itself :lol:

[Jake]

Huh, interesting video. Glad I have a locker rear, I can see where it would be useful, even if I don't get into those type of traction situations much - still nice to have.

Also, I tried mine this morning... it will 100% NOT let you lock it in 2WD. I think Pete's truck is a few years newer so maybe they changed it for the 2013 update.

[Senor_Taylor]

So, truck in 4 lo with the rear diff locked and it still took me 10 minutes of back and forth and shoveling to get out of my spot. At least I made it to work in under an hour. I'm the only person here who didn't sleep here last night.

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[Beej]

Good thread, and thanks!

It got me to look into what the Jeep has (their marketing names aren't the simplest). Apparently it's Quadra-Trac II, which is full time with a center locking diff (lo) and open diffs front and rear. And I dunno how much of it is a gimmick but also Selec-Terrain, which means auto/snow/sand-mud/rock modes. That page says you can get a LS rear (Quadra-Drive II), but apparently it's an option or upper model thing - I don't see it in the compare models thing on Jeep's site.

Didn't really think much about inclement weather when we got it, but it's damn impressive in this stuff. Whatever snow mode does works.

So if you don't have LSD's, I assume modern traction control systems that can brake individual wheels make up some of the difference?

[ScottyB]

So if you don't have LSD's, I assume modern traction control systems that can brake individual wheels make up some of the difference?

definitely. cheap, effective enough at sane speeds and super easy to implement with modern traction/yaw control systems.

the LR Evoque uses this and its pretty impressive how far it'll get on street tires. bump this to 1:00 in, here's a clip of the brake vectoring in action, you get the idea.
[youtube]iw1aT5c1Lus[/youtube]

[Jake]

Modern traction control tech has come so far, it's wild.

Had to use the neighbor's truck today. Mine got hella stuck just backing out of the driveway - the Bridgestone highway tires it has are just trash in deep snow. I got my truck re-parked but later in the day, the snowplow came through and got stuck.

Plow truck was an early-90s Silverado 1500 with generic "all terrain" tires and got stuck right in front of my house.

Neighbor guy is late 20s and has a 99 Silverado with BFG All-Terrain tires. No traction control on his truck and frankly, he didn't know how to drive it. We used my tow strap and pulled the plow truck back enough to get it un-stuck, but then Nate's Silverado was stuck. He drove at first and I was amazed - even in 4 Low, it was happy to sit there and spin one wheel on each axle. Open diffs FTL.

I was able to get it going after judicious use of throttle. Nate's problem was just being scared of anything above 3k rpm. Turns out four people in the bed (for weight), 5k rpm in 2nd and enough yelling of "c'mon bitch gooooo" will get an old Chevy up a snowy hill :thumbup:

I really think my F150 would be fantastic for this stuff if it just had better tires. Nate's truck was leagues better because of the BFG's. But, his tires would suck for extended highway drives which is all I do.

[rherold9]

Separate sets for seasons. If you have the monies of course. Good snow tires like Blizzaks will make any 2wd feel invincible. Would be impossible to get stuck with 4wd and Blizzaks

[Senor_Taylor]

Made good use of all of my features today. I got called into work today and it turns out I'm the only person that could make it. It was me and like 5-7 people that sleep in the hotel right behind. Worked all day and drove someone home just now. Combination of low range and my rear diff locker got me home, until I got to Copper Beech, where they haven't plowed all day. Got stuck and had to dig myself out. I've never hit the rev limiter in my truck before tonight, but I'm sure my truck hates me after having the diff locked and being in low range with the foot to the floor clawing my way out of 25 inches of snow. Got to my house and couldn't even find a near my house that didn't hit a foot wall in front, so here my truck lays until I dig it out again in the morning.

[Jake]

Separate sets for seasons. If you have the monies of course. Good snow tires like Blizzaks will make any 2wd feel invincible. Would be impossible to get stuck with 4wd and Blizzaks

If it snowed more often, I'd care more. My truck is like DJ's, it's used 98% of the time for on-road, highway stuff, and doesn't really merit separate tires.

Not sure Blizzaks would help here either, the more knobby tread of the BFG's were what could dig in to the deep snow and move it. Blizzaks aren't quite so aggressive.

[Ryan T]

I really think my F150 would be fantastic for this stuff if it just had better tires. Nate's truck was leagues better because of the BFG's. But, his tires would suck for extended highway drives which is all I do.

You are spot on here. I've got some pretty aggressive all-terrain tires on my F150 and they SUCK on the interstate. They're loud, wobbly and generally not much fun to drive at 70+mph. They do ok pulling a small utility trailer but they aren't that great for pulling heavy loads either. But get them in the snow or in a muddy field or pulling someone out of a ditch and that is where they really shine!

[ScottyB]

Not sure Blizzaks would help here either, the more knobby tread of the BFG's were what could dig in to the deep snow and move it. Blizzaks aren't quite so aggressive.

its not the aggressiveness of the knobs, its the siping within the tread blocks (all the little cut-lines in the tread) along with compound and tread depth to an extent. mud terrains with big, solid knobs are remarkably poor in the snow for that reason. most snow tires look completely pedestrian going strictly by tread look but the grip is eye opening....there's a lot of weird tech behind compound and tread design for that stuff that seems like it wouldn't work.

[rherold9]

Not sure Blizzaks would help here either, the more knobby tread of the BFG's were what could dig in to the deep snow and move it. Blizzaks aren't quite so aggressive.

its not the aggressiveness of the knobs, its the siping within the tread blocks (all the little cut-lines in the tread) along with compound and tread depth to an extent. mud terrains with big, solid knobs are remarkably poor in the snow for that reason. most snow tires look completely pedestrian going strictly by tread look but the grip is eye opening....there's a lot of weird tech behind compound and tread design for that stuff that seems like it wouldn't work.

Spot on.

Blizzaks or not I can guarantee snow tires would do better than what is on your truck now, Jake. Blizzaks are some of the better snow tires.

Big blocks does not mean better traction for snow.

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[V1GiLaNtE]

I spent the majority of the snow running around in 4high. Tires were aired down to about 20psi and I found myself gliding right over the top. BFG's all terrains are very equipped to handle snow conditions given the siping in them. 4lo was only required during recovery situations to ensure I was able to slowly back somebody off a snow drift or inch them forward enough where they could manage under their own power. No locker required or equipped.

[HAULN-SS]

Got about 36" at my house. F250 in 4lo, put chains on just the rears, had no problems getting around here in WV before they plowed...had to stop a few times and shovel out the pushed up snow in front...could definitely tell a difference when it was locked vs open