As pretty much anyone who offroads knows, AWD vehicles absolutely tear up the trails vs a proper 4wd with lockers, since AWD relies on detecting tirespin (ie, destroying trail) to determine when it needs to activate.
AWD can theoretically work far better than a 4WD with diff locks, because it can simulate, based on the steering wheel angle, the exact speed each wheel should turn, and 'lock' each wheel to that speed giving zero slippage.
Just a shame that the sensor -> computer -> actuator feedback loop seems to be 200 milliseconds or more, so AWD vehicles just end up having different wheels slip semi-at-random till that wheel gets the brakes activated 200ms later.
It’s not just sensors. It’s mainly to avoid it falsely applying itself. In my opinion, that is far more dangerous because it’s wildly unpredictable when it will work as expected vs when it toque vector.
I can get the torque vectoring to do some weird things, kind the right conditions on my car. It’s okay because I’m intentionally pushing the limits, but I absolutely would not want the vectoring to kick in when I’m not expecting it. Towing on packed snow/ice is not the place you want to learn your wheels suddenly decided to react dramatically differently.
Most AWD systems do not have the ability to vector torque like that. They're usually based on mechanical limited-slip differentials that require some amount of slip before they partially lock, and sometimes the limited slip is only between front and rear, not left and right. There are different types, with some requiring a lot of slip before they lock up and others requiring little.
Limited slip differentials cost more than open differentials. Limited-slip differentials that lock up quickly cost more than those that allow a lot of wheelspin. Electronically-controlled torque-vectoring differentials cost yet more.
The system you describe seems to meet the NPS definition of 4WD someone linked elsewhere: "a means to mechanically power both front and rear wheels at the same time", though I wonder if there might be some more technical regulation with specific requirements. I agree that sort of thing could work well for off-road use.
NPS defines 4WD specifically as part time four wheel drive with a transfer case and low range, FWIW. Low range is a big part of it. And yes, their definition technically excludes higher end "full time 4WD" systems in some cases, though I suspect everyone would look the other way at those.
A quick web search didn't find a formal definition, only information pages for specific parks with descriptions. I agree it's likely park rangers would use common sense in practice such that a vehicle with an extremely low first couple of gears, lockable differentials, appropriate clearance, and suitable tires wouldn't get cited as "not 4WD" because it doesn't have a selectable 2WD mode.
Incidentally, I once owned a Subaru from the 1980s which had a lockable center differential and separate high/low gearshift, which was synchronized and could be shifted in motion. It was not designed for serious off-road use, illustrating the folly of relying on criteria like these.
> A Jeep, sport utility vehicle (SUV), or truck type with at least 15-inch tire rims and at least eight inches of clearance from the lowest point of the frame, body, suspension, or differential to the ground. Four wheel drive vehicles have a driveshaft that can directly power each wheel at the same time and a transfer case that can shift between powering two wheel or four wheels in low or high gear. All wheel drive (AWD) vehicles do not meet this definition.
I completely agree they'll use their discretion, but either way, that definition is specifically a part time 4WD system with low range.
AWD has come a long way in that regard in the last few years. It's still highly variable from manufacturer to manufacturer, but systems that use internal clutches alongside brakes (and not only brakes) to control wheel movement + tight feedback loops can really do a great job of minimizing wheel spin.
They get a lot of hate, but the bronco sport has the best AWD system I've driven to date in that regard.
And with that said, it is still the type of thing the Park Service would rightfully cite as not a proper 4wd. 9ish inches of clearance is not much, and the lack of a low range will bite you. I've taken mine on plenty of milder 4wd only trails in parks (e.g. black gap in big bend plus tons and tons of forest service roads), but I'm certainly not going to do elephant hill in canyonlands with it. That's what the dedicated off-road rig is for.
There are "4wd only" trails in national parks that high clearance AWD is fine on. The rangers will tell you which ones those are.
Canyonlands is a different beast than most national parks. Canyonlands has some very gnarly trails open if you have a permit. Lookup dollhouse sometime. Beautiful, but insanely technical. Elephant hill is better known and a bit milder.
From their report of "the little three-, two- and (very occasionally) one-wheel-yeet maneuver", it sounds like the lack of suspension travel was the main issue. The details of your AWD or 4WD system don't matter as much if you can keep your wheels on the ground.
Still, just because they were fine doesn't mean someone else would have been. The main risk seems like doing a somewhat technical, off-the-beaten-path trail alone regardless of your vehicle's capabilities.
Yeah, I came across that earlier. Definitely impressive!!
I completely agree with your general point (articulation matters a ton!) but I have to take a bit of issue with:
> "The details of your AWD or 4WD system don't matter as much if you can keep your wheels on the ground."
That's where the details of the system matter the most. Getting torque to a single tire is the hard part and the reason folks focus on it so much. A _very good_ AWD system can get enough torque to move the vehicle uphill / out of a tough system to a _single wheel_. Most can't. Most traditional part-time 4WD systems can't either. Open front and rear diffs are the norm in "true 4wd". Locking rear diffs are starting to become commonplace, but only a few stock vehicles come "triple locked" from the factory.
I grew up wheeling an old mid 80's S10 Blazer. Fun, small, fit down trails well, had the "holy grail" 100" wheelbase. Solid rear axle + IFS. Manual transmission. Good (enough) articulation. Plenty of clearance. Big enough tires. Crap horsepower. Worse gas milage. "True" part time 4wd with a transfer case (i.e. would 100% meet the NPS's definition in this case). But open front and rear diffs. I got stuck every time I got a tire off the ground.
I've taken the little bronco sport plenty of places I tried but could never make it in the Blazer. (And to be fair, vice versa... Big muddy ruts are not something I want to put the sport through for clearance reasons, and that's kinda what the Blazer did best.) At any rate, good modern AWD can often beat traditional part time 4wd with open front/rear diffs when wheel lift comes into play. On the flip side, independent suspension all around means it's going to lift tires _all the time_, so it _has_ to be good at it. Most AWD systems unfortunately aren't, even though some are these days.
