New trucks and 4low...
- Thread starter rho
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DaveInDenver
Middle Income Semi-Redneck
Of course low range has almost no purpose for driving on snow packed and icy pavement. I guess if a buyer doesn't know why they'd want low range they probably don't actually need it. However a truck destined for use off highway it's not really a nice (ETA: meant to say critical) to have feature, though I doubt most people who are greenhorns would know why. So for them not having it and not knowing how to use it would lead to using too much speed and not much control in technical situations.
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MOguy
Explorer
I will agree if you are building a daily driver to run around on paved roads 99% of the time. I had a 4 gen 4Runner that had the AWD and Regular 4wd high and low. The 4Runner had an engine/brake management system that worked well in packed, icey snow but you could not turn it off. This made it suck butt off road. I have had other vehicles with traditional 4wd.
On slick paved roads the AWD is ideal, the traction control stuff does work well in snowy conditions but rougher off-road it sucks. If you are running simple fire roads and trails you will be fine but if you run anything challenging the auto stuff can work against you.
Having your brakes and motor make decisions for you can be advantageous certain times but can screw you up others. Being able to control the power you put to the wheels is necessary for some tougher obstacles and mud. Having the motor or brakes control wheel spin can work against you in some situations. In muddy conditions wheel spin is essential to clean out your tires.
Having a LOW gear can also help you maintain control when climbing rougher train and buy allowing the engine to control your speed and not requiring as much braking.
For me I would never consider an AWD vehicle for this activity. I would have no issue with an AWD as an option but still want traditional 4wd hi and low. I have no issue with traction control as long as you can turn it off.
I also have a Acadia Denali with all wheel drive, I am sure it is a different set up than you Yukon. It does work find on snowy slick maintained roads. Great Vehicle for road trips but I would NEVER considerate for the activities discussed in this forum.
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Buliwyf
Viking with a Hammer
For me, I notice that most of the AWD + comments are on paved or gravel roads. Where I nearly never need more than 2wd. And for the rare icy hill climb, 4WD is fine.
4L offers me something positive, AWD offers me nothing. Hopefully AWD sticks to SUV's and Honda's, and HD trucks remain a proper 4WD. There's no way I'd give up 4L for AWD.
Not to mention, on a slick snowy hwy, I have noticed improved braking distance in 4WD. About one truck length, because one axle prevents the other from locking, just a little bit. AWD doesn't offer that.
4L offers me something positive, AWD offers me nothing. Hopefully AWD sticks to SUV's and Honda's, and HD trucks remain a proper 4WD. There's no way I'd give up 4L for AWD.
Not to mention, on a slick snowy hwy, I have noticed improved braking distance in 4WD. About one truck length, because one axle prevents the other from locking, just a little bit. AWD doesn't offer that.
shade
Well-known member
A friend of mine bought a Jeep Rubicon and proudly showed me it had stabilizer bar disconnect switches. He had no idea what they were for, but he sure was excited about flipping them. After several years of ownership, that Rubicon has never driven over anything rougher than a gravel driveway.
I believe some AutoAWD systems have clutch packs somewhere that will wear out. Not a big deal on pavement, but I doubt they'd fair well offroad over long, hard use. Before buying an AutoAWD vehicle I intended to drive offroad, I'd want to know how it worked, and how it was disabled. I know the various ABS-derived traction aids on my truck can be confusing, but I can turn them on & off at will. Canned terrain systems probably don't allow that level of control.
shade
Well-known member
On heavier vehicles, I think wear and complexity issues will keep AWD at bay.
rho
Lost again
Agreed. Auto4wd is labeled as useful on road when conditions are unpredicable like severe rain or snow but when 4hi is overkill. Because it doesn't fully lock it makes steering easy and doesn't cause bind like 4hi or 4lo do. I find it VERY helpful during winter when roads are slick, especially with an empty bed. But the AutoTrac (GM) system isn't new. My old '01 GMC Sierra Z71 had it.
Fancy seeing you here! A bunch of the GMT800 trucks I've been working on all have it, I'd prefer a manual Tcase myself in a truck but I'm old fashioned, heh. At least the auto locker in those trucks is predictable.
luthj
Engineer In Residence
Locked center diff 4WD is a liability at speed, especially on mixed surfaces. Open center diffs actually tend to improve response, and reduce the risk of oversteer on nominally RWD vehicles. Of course that is also generally reffered to as AWD. Though there are many vehicles that use a clutch to apply front/rear axle power and use the AWD term.
The computer controls are much faster than a human, and when fractions of a second count, the AWD systems have the edge. You can't just flip from 2WD to 4WD at the drop of a hat in a manual shift system. The references to off-road safety have some merit, but again, how many ExPo members spend more than a few percent of their time in 4WD? I would bet the vast majority are on pavement, ice/snow/rain possibly, or maybe improved dirt roads at least 95% of their miles.
The computer controls are much faster than a human, and when fractions of a second count, the AWD systems have the edge. You can't just flip from 2WD to 4WD at the drop of a hat in a manual shift system. The references to off-road safety have some merit, but again, how many ExPo members spend more than a few percent of their time in 4WD? I would bet the vast majority are on pavement, ice/snow/rain possibly, or maybe improved dirt roads at least 95% of their miles.
XJLI
Adventurer
Shift on the fly has been a thing for quite some time now...
shade
Well-known member
True.
He's talking about millisecond shifts made to individual wheels in an active AWD system. It's not humanly possible to do that, even if the system allowed that level of manual control.
DaveInDenver
Middle Income Semi-Redneck
With the front hubs locked most manual cases have no trouble shifting on the fly at any speed. That's has been the case with Toyotas as far back at 1979. Momentarily letting up on the throttle and the shifter will move the front drive collar basically effortlessly. It's not as quick reacting as a mechanical limited slip or ABS/traction control though.luthj said:
Most center diffs I think are Torsen type 3 (I know that's what Toyota is using anyway), so aren't clutches or need LSD modifiers. They just work, no need to rebuild or replace anything. I don't know if GM has gone a different way or have added the clutch to further fine tune the torque split for different conditions. Theshade said:
Torsen action can change with a different weight lube or slightly with different brands since it works based on friction of the gears to the case, but the function itself is fixed, which is the negative @luthj is talking about. If the rear wheels slip it can't unpower them. The center diff is just there to let you run (well turn really) 4WD on pavement without binding so you (or typically the traction control for you) still need to take some care to drive correctly.
Which, FWIW, is why I think Toyota hasn't put one in a pickup. It's hard to come up with algorithms for TRAC that effectively works with a pickup that might be empty, might be full, might have all sorts of different loads and wheelbases. An SUV is more fixed in weight distribution and dimensions so the range of reactions that must be predicted I imagine are easier to accommodate.
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shade
Well-known member
I was thinking more about the on-demand systems that shift torque to the rear wheels, like Honda uses. Also the L/R split used in some torque vectoring systems. Like I said, I'd want to know exactly what was going on before buying an AWD system.
jacobconroy
Hillbilly of Leisure
Yeah, that's what made me fall in love with my little Jeep about 11 years ago. It is the first (and only) rig I've owned that doesn't have manual hubs. Going from 2WD to 4H at 30 MPH in a blizzard is really nice...and if the roads is better 10 miles later, just switch back to 2WD.
I'll admit that a computer doing all that for you would be even easier...but I like to be the one making the decisions when it comes to driving. Not sure what the "ESP" really does in my Jeep, but I purposely disabled it when the Jeep was two years old after the first time I started fishtailing around on ice due to that stupid computer deciding that I was out of control when I wasn't out of control. All I could tell is that the Jeep was braking wheels independently. Aint havin' that ********.
Been getting by just fine without it.
DaveInDenver
Middle Income Semi-Redneck
That's where the knucklehead in the operator's position has to predict things. You want to shift on the fly into 4WD before you need it so you don't slip. It's why I think there's more accidents now on snowy roads (the invincibility effect aside). All auto 4WD or AWD systems are reactive, you're already starting to spin and the system is trying to unf*ck things. If you're a level headed driver (as we all are, no doubt) and knew when to go in and out of 4WD you never need the traction control to do it for you. Naturally you also drove circles in parking lots on snow days to get the feel of your truck and know how if you have engaged 4WD and are still starting the spin or drift you knew how letting off the gas and steering would get you straight again. Of course now the car does all of this for you so you never learned nor practiced. So as long as your particular spin matches the designed parameters it works. When it doesn't, welcome to the ditch!