AWD vs 4WD

I know tundras dont have this...but I had a guy tell me he has AWD in his Chevy in auto and the 4WD when he puts it in it...is this so? I always thought AWD is all 4 spinning at same rate as much as 4WD is. Any help is appreciated.

 

I have 2wd. But if I don't engage it then I have RWD.

Outside of the details of front vs rear torque distribution, AWD or 4WD engaged is the same thing. AWD doesn't turn on or off, it's full time, all the time. 4WD is manually selectable, except for rare cases like the Honda "real time 4WD" system which engages the rear wheels only when the front wheels slip.

Either your buddy was trying to confuse you, or he bought a line from the salesman, or maybe hes calling 4LO "4WD". Regardless, he drives a Chevy so whatever he says is wrong by default.

 

Not trying to wrong, but with research they are saying AWD sends power to which wheel needs it and 4WD is even power to each wheel. I am just trying to see an explanation of this because I thought AWD was constant like 4WD but would make sense as to why AWD can get better fuel economy to 4WD, though not much different. But I guess I will have question as to how old system we are talking. Guy with Chevy Silverado 2016 6.2L Z71 series. Just wanting clarification as to I'm dumb or to he got told a lie based of the simple knowledge I have. Thanks to anyone with help.

 

Which I guess you are saying in layman's terms is unless it senses you dont need AWD but 4WD is selected you have it?

 

It’s probably 2wd with a AWD and a locking transfer case. Which would then turn it to 4WD.

 

That's why I said outside of the details of torque distribution. There are so many styles and variants of all wheel drive. Some split equal distribution front to rear, some can go 60/40, 70/30 and so on depending on what the car is going through. Look into Subaru, Audi, or even Nissan awd systems and you'll see they aren't all quite the same. If you really want to see an oddball look up the VW beetle 4wd from the 40s (yeah they made them back then) with low range hubs, very wicked engineering for the time.


Generally, AWD is a fulltime affair. 4WD can be turned on and off at will. It takes more energy to spin 4 tires than 2, so fuel economy drops. Check fuel economy of any car that comes in 2wd or AWD and you'll notice the advertised MPG will be higher on 2wd.

I rented a Tahoe a few years ago with an annoying 4WD system. It could be driven in 2WD, or 4WD if I engaged it, or what I can only describe as "2WD unless you lose traction and then 4WD will engage" mode. I didn't like it because it was harder to anticipate on icy roads in that mode, so I either kept it in 2WD or in bad areas went 4WD.

I have a Honda Element with a very similar system, it goes 4WD by itself if I am stuck but is otherwise front wheel drive. It uses wheel speed sensors and if the front wheel speed out runs the rears, a clutch in the rear diff engages and I start moving. I cannot however decide to put it into 4WD.

 

First off, they are all marketing terms so them mean different things to different brands so there will be an exception to any definition you hear of 4xx, AWD or 4WD.

Generally speaking however...AWD vehicles have a viscous center differential. This acts like a LSD, in that it allows your front and back wheels to move at different speeds to a certain degree, but the greater the difference the harder the fluid in the in the center diff becomes until it locks the front and read drivetrains.

USUALLY, (but not always) these vehicle have a forward torque bias where they will be 80/20...until the back wheels slip enough at which point they will become 50/50. Some, are always 50/50 but allow slippage when needed for smooth cornering.

These vehicles actually can have EVERY wheel spinning at a different rate than the others.

4WD usually means no center diff so that when in 4WD the front and back wheels are locked so you will always have at least one wheel on the front, and one wheel on the rear, moving at the same speed no matter what. These vehicles will always skid slightly when cornering but not as bad because they still have open diffs front and rear so each axle can split its torque side to side.

4x4 usually means all wheels turn at the same speed no matter what and will skid any wheel that needs to move a different speed than the others.

It is completely possibly to have an AWD vehicle with a LSD center diff that has the option to be locked, although most do it automatically.

In short...AWD is the easiest and smoothest to drive....while 4x4 gives you maximum traction...and 4WD is halfway between.

 

"If you really want to see an oddball look up the VW beetle 4wd from the 40s (yeah they made them back then) with low range hubs, very wicked engineering for the time. "

I wish mine was 4WD....but I have great respect for VW's This is mine. The only 2WD vehicle I own.



(1967 1600 DP engine, 1970 IRS manual tranny and front end)

 

Holy shit, the more I watch this the funnier it gets!

 

First time I've read that 4WD and 4x4 are not two ways of referring to the same thing.

 

Guys with locking differentials will be more than happy to tell you that you only have a 'true' 4x4 if you have locking diffs and everyone else just has 4WD.

But like I said....these terms where all just marketing terminology at one point and have gotten so mixed and matched that they don't mean much except in the comment section of internet articles.

 

Some Chevy full sized trucks do indeed come with selectable AWD/4WD.

 

Gm auto mode is very nice to have. Beats the tundra system. Now for the rest of the truck not so much. In auto there’s no slipping in slush or wet roads. Very nice feature. Hope the next gen Tundra has it. Then I would upgrade in a heartbeat.

 

Here, I like this guy, good learning

https://youtu.be/47m7QAPrpsI

https://youtu.be/BMv_v9IBugU

 

I like it! My first VW, first car, was a 65 baja and it was so rough but capable. I wish I had pics or better yet videos of that thing. The rest of the VWs in my life have been street but I've been itching for another baja.

The 4WD KDF are beyond rare, I believe under a thousand were made but it's been 20 years since I studied VW history. They shared drivetrain with the Kubels.

 

This. My 2004 Z71 had 3 modes for 4WD - Auto, 4HI, and 4LO. Auto mode was perfect when driving in the rain or otherwise slippery road conditions. It is a feature I miss, along with the power folding mirrors.

 

Didn't someone on here swap a transfer case from a sequoia and get auto FWD. My wife's GX 460 has it.

 

Randomly stumbled on this thread. GM, Ram and Ford all have AWD transfer cases. They are not Automatic 4x4, meaning the 4x4 engages automatically. They are Borg Warner transfer cases with clutches that can continuously vary torque to the front wheels on the fly up from 0%:100% to 50%:50%. They can also lock into 4x4 hi or lo just like a regular T-case.

Its great when you are on pavement in crappy conditions where you may be passing from dry pavement to snow, back and forth all the time.

 

There are a few out there. The Sequoia TC has 2WD to 4WD functionality identical to the Tundra with the addition of having the selectable Torsen locking/unlocking center differential like the full time AWD Land Cruisers in both high and low ranges. Last I read is that Toyota owns this but licenses it out for use by other manufacturers. The best of both worlds.
https://www.awdwiki.com/en/toyota/#Land_Cruiser_200_V8
https://en.wikipedia.org/wiki/Torsen#Center

 

I have the Torsen center in my Lexus GX and it is awesome.

 

Aren't those set up permanent AWD like the LCs?

Edit:
Just looked it up in one of the links I posted above. Yep. AKA Land Cruiser Prado in other markets.

 

It's all in the transfer case. Torsens are cool in that one shaft can go faster but just not slower. These are full time AWD, the least efficient, and can be locked. Borg Warner has a transfer case found in trucks that use clutches and electromagnets to transfer some torque to the front shaft and if it senses rear wheel slippage more torque until 50/50. I would call this part time AWD and can be "kind of" locked by applying max pressure to the clutch plates. This setup is fuel efficient and works great (but maybe not rock crawler over-landing great).

We have the oldest style of 4x4 transfer case which is either locked or unlocked with no in-between. I had a F150 with the part-time AWD transfer case and it worked really great on snowy highways. I don't rock-crawl in my truck so I never overstressed the system. Toyota could have used that same BW transfer case but chose not to probably because it's less efficient (fluid coupling even in 2WD). The one we use can be found in Ford XLT's and below.

 

I learned about the Tundra 4x4 the hard way. I bought my 2008 DCLB used and the owner didn't know anything about the system either. I engaged the 4 Lo and proceeded to do some u-turns in his cul de sac, the poor truck was whining and groaning the whole time! I thought it was broken and I'm damn lucky I didn't actually break it. Bought it anyway since it worked ok in 2WD.

Since then I've found out never to run this thing in 4WD unless:
1) You're headed down a straight road with moderate speed, then it's safe to run 4WD Hi. Usually I do this just to keep the system lubed, it's part of the specified maintenance in fact
2) If it's actually slippery then run 4WD Hi and you may turn. Slippery = Mud, snow, sand. Wet asphalt doesn't count, the front wheels will bind
3) I run 4WD Lo only when I wish to make sure it's still working. I'm not taking this thing to Moab. Don't do u-turns in your suburb!

 

https://www.caranddriver.com/features/a27630736/awd-vs-4wd/