Why your SUV sucks in the mountains

[AK47bp]

My SUV doesn't suck, you suck!

[Norseman]

You're a towel!

[Bobcat Sig]

My SUV doesn't suck, you suck!

This...

You're a towel!

... and this.

The lulz

[bodywhomper]

there are some recent generalizations in this thread about how 4wd, awd, full time 4wd function.

my understanding is that different electronic traction control systems among manufactures function differently. for example, there are several posts earlier this fall in another thread (or 2?) from jamal where he dives into a ton of detail about the various traction control systems from subaru over the past decade or two.

to clarify about an "open differential." a vehicle in 4wd/awd/full time 4wd. etc. with an open differential and without an electronic traction control system, a mechanical limited slip differential, and/or the center differential locked will put power to only 1 wheel. if you have a tire with less traction than the other 3 tires, that single tire will receive all power from the engine and the 3 other tires will receive no power.

an example: i have a 1999 land cruiser that is "full time 4wd." it has no electronic traction control and no limited slip differential. unless i have a differential mechanically locked (it's a switch on the dash), it has an open differential and will put power to only one tire. when i'm driving on open roads/trails with traction issues (e.g. dirt, gravel, ice, snow, sometimes water), i will often lock the center differential for improved traction. i even often do this when creeping on the half mile residential dirt road that i love on because of the steep hills and the tendency for washerboarding to occur (more traction will reduce tire spin and the washerboard affects on the hill). On windier roads/trails, i may or may not lock the center diff, depending on the roadway conditions and turn tightness.

[GPP33]

So getting this thread back on track to arguing about 2wd vs 4/AWD....I think most of the cluster fucks I've been stuck in were a result of people not being able to drive up the hill, not that they they couldn't stop when they needed to. Sometimes traffic briefly stops because some dimwit spins out but the congestion comes when the other 99.9999% of the people can't get moving again. It would be interesting to see some data behind closures/major traffic incidents and what the cause was. East bound I-70 from Dillon to the tunnel is always a getting moving problem, not a stopping problem.

[bodywhomper]

Contrary to that^^, my experience in CA are that the worst goat rodeos were about people not being able to slow down or stop. Multi car pile-ups on I-80, 88, 89, 395. Some of the worst are from rapidly changing surface conditions involving big rigs at an elevation below the tire chain requirement (ie roads suddenly got slick and all the trucks (and others) are not driving with tire chains.

[optics]

Contrary to that^^, my experience in CA are that the worst goat rodeos were about people not being able to slow down or stop. Multi car pile-ups on I-80, 88, 89, 395. Some of the worst are from rapidly changing surface conditions involving big rigs at an elevation below the tire chain requirement (ie roads suddenly got slick and all the trucks (and others) are not driving with tire chains.

Although, in certain situations, the combination of another vehicle's inability to stop - along with your own ability to accelerate rapidly - does start to make AWD important again....

I've had a few "that guy in my rear view is going sideways, I gotta gun it outta this spot right now" moments where I was happy to be on my hakkas. (and in an suv, FWIW)

Traction (accelerating and decelerating) + position (relative to other vehicles) is the key, right?

To the OP/subject line: I've ended up on mormon emigrant trail a couple of times when it probably should not have been open and was unplowed, but you didn't hit that unplowed stuff until a few miles in. In that situation I was very glad to be in an SUV with more ground clearance and with real winter tires (severe winter not M+S). I've had lots of good AWD wagons (allroads etc) over the years and even with good snows, I prefer an SUV for times like that.

[auvgeek]

Yeah, IME the scariest accidents happen at speed. Yours or someone else's.

Stop light at the bottom of the hill is a big one where 4\AWD is of limited use -- tires and skill (downshifting instead of braking, etc) are the name of the game.

[XXX-er]

Contrary to that^^, my experience in CA are that the worst goat rodeos were about people not being able to slow down or stop. Multi car pile-ups on I-80, 88, 89, 395. Some of the worst are from rapidly changing surface conditions involving big rigs at an elevation below the tire chain requirement (ie roads suddenly got slick and all the trucks (and others) are not driving with tire chains.

driving due narth on hy 97 thru northern BC with the arctic front moving down NA one could be on a clear/wet road with no snow and 10kms down the road its black ice at which point trucks or SUV were screwed if they didnt clue into the ice, so I got in the habit of nailing the brakes every so often at highway speed to see if the road was frozen

not really much traffic on that highway for the amount of 4x4 SUV and b-trains you would see off the road

once you were in the shit a car that will handle with studs had the best chance of getting out of the shit

-30 or -40 , engines not starting, breaking plastic body parts, rusting bodies, compared to down south it was a whole nuther level of bad road/hard on a vehical

[jamal]

to clarify about an "open differential." a vehicle in 4wd/awd/full time 4wd. etc. with an open differential and without an electronic traction control system, a mechanical limited slip differential, and/or the center differential locked will put power to only 1 wheel. if you have a tire with less traction than the other 3 tires, that single tire will receive all power from the engine and the 3 other tires will receive no power.

It's not so much that the 1 wheel gets all the power, it's that all the wheels get the same amount, regardless of the traction they may or may not have. So a wheel on ice with "zero" traction gets zero power. Which means the wheel on the other side gets zero power. Which means the engine generates zero power, no matter how hard you floor it.


Referring to an earlier post, I'm not sure what the benefit would be of an open center vs locked 4wd on a slippery surface, regardless of speed/conditions.

[bodywhomper]

Thanks! My terminology and understanding are a bit flawed. “Torque” is a better term.

Wikipedia has a good and simple explanation:
-open diff: equal torque, unequal rotational speed of the wheels
-locked differential: unequal torque, equal rotational speed.

If one axle has little friction and the other axle has more friction to the roadway surface, then you’d be able to have better traction with a locked center diff than an open diff, right?

[jamal]

Yeah i like to use torque because it helps you ignore if the wheels are spinning or not. Torque is the actual twisting force, power is the application of that over time. So, technically with one wheel spinning, that wheel does get "all" the power, but I don't think it describes what's going on very well.

For the other part, right. The open diff can't create a split other than 50:50 and can't transfer any torque to wheels with traction. Having diffs locked means whatever wheel(s) have the most traction are going to get the most torque.

[blackalps]

tl;dr: locked diffs are awesome for getting unstuck

[HankScorpio]

i really want an Audi but two nightmarish summer roadtrips in a Passat wagon with endless electrical and mechanical problems make me squeamish about vw/Audi.

I've owned a bunch of Audis and VWs over the years. Yes, Audis and VWs used to be electrical and mechanical nightmares BUT the last 4 VWs my wife and I owned have been extremely reliable for the most part. Also, the new VW warranty is damn good, as is the CPO Audi warranty. I'm convinced Audi/VW have become much more reliable but I would never get one without a solid warranty.

Back to snow tires, I've been getting by just fine with a my FWD GTI with General Altimax Arctics for a while. Less than $100/tire, German made, lots of tread life. Got them mounted to a steel of black steelies for under $600 shipped from TireRack. The few times I've gotten stuck has only been in deeper snow.

FWD with snow tires is completely adequate for around here but my wife's AWD snow tire equipped wagon is the go to vehicle if I'm driving in a snow storm.

[GeezerSteve]

extremely reliable for the most part

? ? ? ?

[El Chupacabra]

I've owned a bunch of Audis and VWs over the years. Yes, Audis and VWs used to be electrical and mechanical nightmares BUT the last 4 VWs my wife and I owned have been extremely reliable for the most part. Also, the new VW warranty is damn good, as is the CPO Audi warranty. I'm convinced Audi/VW have become much more reliable but I would never get one without a solid warranty

Over what period of time did you own the "last 4 VWs"?

How do you reconcile "extremely reliable" with "for the most part" and with "I would never get one without a solid warranty"?

[anotherVTskibum]

tl;dr: locked diffs are awesome for really stuck

FTFY.

[HankScorpio]

Over what period of time did you own the "last 4 VWs"?

How do you reconcile "extremely reliable" with "for the most part" and with "I would never get one without a solid warranty"?

We had/have a last gen '11 Touareg, '11 Jetta wagon, '15 GTI and '17 Alltrak. "extremely reliable for the most part" was a poor choice of words. They were all reliable other than 2 recalls (water pump on GTI and faulty sensor on the Touareg).

Also had 2 A4s (98 and 05) which were complete money pit disasters.

Any used car needs to come with a warranty for me.

[El Chupacabra]

We had/have a last gen '11 Touareg, '11 Jetta wagon, '15 GTI and '17 Alltrak.

Were the two '11s replaced by the '15 and '17?

[HankScorpio]

Were the two '11s replaced by the '15 and '17?

The '11 Jetta wagon was traded for a GTI. The Touareg (which I kick myself for trading in) was traded in for a Volvo V60 but we ditched that in favor of the Alltrack.

[bodywhomper]

You all go through cars quick!! For me, reliability is related to shit working in the long view, like more than 10 years later.

tl;dr: locked diffs are awesome for getting unstuck

There seems to be a supportable argument related to improved safety for emergency handling for locking the center diff in compromised traction situations. See the later half of this vid
https://youtu.be/EBmw6Wpfe6M

If I’m off base about this, I’d appreciate knowing.

Back when I had an 88 4Runner with auto hubs, if the truck was in 4wd, the center diff was locked. There were times where I’d drive hundreds of highway miles in mixed road conditions in 4wd (as required by CHP) without problems.

[mall walker]

in 13" of fresh I was wishing for some snows today... not sure that would've helped my 8.7" clearance but it couldn't have hurt!

[summit]

There seems to be a supportable argument related to improved safety for emergency handling for locking the center diff in compromised traction situations. See the later half of this vid
https://youtu.be/EBmw6Wpfe6M

If I’m off base about this, I’d appreciate knowing.

I have to disagree. One of the comments in the video covers it extensively:

1. Locked center offers less directional control on any surface in order to gain surety of traction in complex uneven terrain (ie the example with the front axle high with a wheel fully off the ground. The second example is RWD truck vs truck in 4WD (locked center).
2. That's why rally racers use AWD (FT-4WD). You see subies and audis... if a locked center was better, they'd use it.
3. The logical progression to validate this thought is adding yet another locker (rear locker) think about what that does, now go back to the center lock quandary.

I believe snow driving is more analogous to rally than to proper 4-wheeling... until you get into deep unplowed or stuck in the ditch.

Hi Mr Andrew. Congratulations for the video. I like very much your training videos and I consider you a Master Class in 4x4 world. However, I'm not totally agree with the explanation. According to you, Full Time 4WD is the very same that 2WD in most situations because of the fact that, in both 2WD or FT-4WD if you lift a wheel off the ground the car is instantly stuck. Ok, this is true when you are off roading in very irregular grounds, but the tyre behavior in terms of traction is not a matter of all or nothing, always or almost always there is an amount of traction on each wheel, even on snow, gravel, wet pavement, etc, and there are really very few situations in which one wheel loses all traction, like lifted off the ground. If you drive a 2WD car on wet pavement, the most of the time the car will keep moving and it only will get stuck if one wheel loses too much traction, but if you drive the same car in FT-4WD you significantly increase the traction, sending the power of the engine to the 4 wheels. Certainly, even in FT-4WD if you lift only one wheel, you will get stuck like in 2WD, but keeping a very small traction by wheel, FT-4WD greatly improve the movement and safety.

If not, what is the reasoning of the Full Time? The best cars in the World Rally Championship are 4WD from the begining. In 1973 a 4WD Jeep Wagoneer AKA Moby Dick won a rally competition where the rest of the competitors were 2WD sport cars.
From my experience. I have a Jeep Liberty KJ with Command-Trac system from factory (2H - 4H Part-Time - 4L). A time ago I decided to change the transfer case from NV231 to NV242 with Full-Time because of the improvement claimed by owners in rainy and snowy roads. Well, the improvement was greatly and not only on wet pavement. Before, when off roading, because of the 4WD, for taking curves with small radius I needed to go back and repeat the manuever to exit the corner even in a car with a good steering radius, and now I enter and exit the corner in one maneuver.

On the road, this car has a rear LSD from factory and I must say that driving a rear 2WD with LSD on twisted wet roas is like dancing and you have to modulate the gas pedal very careful. Ask to the BMW owners. Jeje... When you drive a car in 4WD center locked, the car always try to go strait even when you slightly turn the wheels and it can get a lot worse on wet or ice. When you drive in Full-Time on wet:

CONS: the traction in every wheel is certainly not 100% and depends on the three open differentials.
PROS: the car goes exactly where you drive it.

If you think about a car with ESP on the road, Its main characteristic is braking differents wheels in different moments of a situation to keep the car in control in the middle of a corner so if you force your four wheels to turn at the same speed putting 4WD center locked, I think you are worsening the behavior of the car in many situations, even in off road and I think it will behave better in FT-4WD. This is the same reason why is not a good idea driving on dry pavement with axle lockers on.

I think that every position is good for something:
2WD to improve mileage in dry roads.
FT-4WD to improve traction on roads with wet-dry situations when you can't use 4WD all the time.
4WD for gravel roads and light off-road without climbing, rocks, etc.
4L for fun.
Here is a very good Toyota 4WD training video that can help to clarify all of this questions.

[KyleLanTheman]

^^^ Just pickin' nits, but dedicated rally cars use a limited slip center differential that is likely complex, expensive, and adjustable offering best of both worlds between an open diff and a locked diff. Today's road-going subies and audis have somethin similar. If you want lateral traction and stability, an open diff allows just that. If you want maximum forward traction, locked diffs are the best option. Limited slip differentials allow both.

[summit]

If you want lateral traction and stability, an open diff allows just that. If you want maximum forward traction, locked diffs are the best option.

Best summary