Quote:
Originally Posted by brulaz
Since the OP is primarily considering an AWD SUV, this probably isn't a concern, but many truck purchasers are unaware that the traditional 4x4 is not something you can run on dry or even most wet pavements. It needs very slippery conditions to allow differential wheel spin as it lacks a centre differential.
4x4 is truly an off-pavement or deep snow feature only.
I've never found 4x4 that useful on Ontario highways in the winter as they are usually cleared and salted quickly and so are often only partially snow covered with occasional icy patches. One night our rural highway had enough fresh snow on it to look pure white. I switched to 4x4 and unfortunately baked the centre transfer case right good on the way home. Too much traction!
It used to be that "full-time" AWD (Suburu, VW-Audi, and others) was the gold standard, I think because early "on-demand" AWD was slow to switch, making it only good at lower speeds for getting you out of a ditch.
However newer "on-demand" AWD drive systems are supposed to be very good, even at highway speeds, instantaneously putting traction where you need it, when you need it. I've been told that with the increasing demands of fuel efficiency, and with the improvements in "on-demand" AWD, some vehicles (VW's Touareg) are switching from "full-time" to "on-demand" AWD.
For those interested in pickups, an "on-demand" AWD is now available in some Ford F150 models, like the one Bill described in the Ford Expedition. That's something that I would find more useful than 4x4 on Ontario's highways in the winter.
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Long winded rebuttal based on my experience...
I hope no one feels I am slamming anyone. But my experience seems to be a lot different than others. In the interest of completeness, I provide some real life experience with 4WD (4x4).
My 4WD (aka 4x4) has the following choices:
2WD high range
4WD high range
4WD low range
Automatic 2WD/4WD
Salt can not be used on the roads of California. We have laws against that. Very bad for the environment.
I don't know how much snow they got on Sunday, but it left 9 inches of rain at my mothers house. She lives at 2,000 feet and the pass is at 9,000 feet. Is there a rule of thumb to translate inches of rain into feet of powder?
Several years ago people were abandoning their cars on I80 near Donner Summit. If it was a low sports car then it was buried in snow and not visible to any vehicle approaching from the rear towards it. This, obviously, results in a collision. If you are not prepared to rear end a car that you can not see then you should not be there.
The tread on my truck tires are much more aggressive than the tires on my Lexus SUV. That helps a lot in snowy conditions. In icy conditions it does not matter. On some roads the only thing you can drive is 4WD with chains. 4WD/AWD with M+S tires will be stopped if they do not have chains.
I am well aware of the binding problem when driving on dry paved roads in 4WD. That is why I use 2WD on the highway. I once had binding problems even on dirt roads because, due to a flat in the middle of nowhere, I had to run different size tires front and rear. This caused binding.
posi-trac is helpful in the rear, but in the front it would cause the wheels to run straight ahead. That was 1971. My 2002 and 2008 trucks do not have that problem.
The last time I drove on a plowed road I was back far enough that I could not see the plow. The height of the snow in the plowed area was deep enough to partly cover my headlights on my truck. That would be about waist deep. The snow on the side of the plowed area was about 4 feet deep.
The deepest powder I have ever driven in was at the top of the hood. I'll drive that deep any day in my truck, but not in the Lexus. That depth would be on the Lexus windshield.
It is a real challenge to drive on unplowed side roads when the visibility is 100 feet. I like the visibility I get from the high ride height of my truck versus most SUVs.
Muddy off camber dirt roads with even a few inches of snow are not a good place to be with an AWD SUV. The rocks in the dirt that prevent you from sliding sideways are very tough on the typical SUV tire. Some LT tires with an aggressive tread might work, but I don't think there is enough clearance with the 20 inch wheels.
My brother-in-law used to plow Donner Summit. With his CalTrans ID he can get past the checkpoints even when the road is closed. An unplowed Interstate must be a very interesting place to drive. But that is not a typical situation.
Where I go in the Spring, Summer and Fall, you will get stuck in 2WD, even when not towing. If you can not slide on your back from one side to the other under the TV, then you will get stuck. I had to beef up the battery tray on the TM 2720 so that when it hits a rock it digs the rock out of the dirt instead of bending the brackets.
I wish the TM had air lift suspension so I could lower it to the present 7 feet for storage in my garage, but lift it up a couple of inches when I tow it into the campgrounds I like to go to. I have discovered that when driving through a creek bed, as tires approach the bottom of the creek bed the rear of the TM gets very close to the ground. The rear hitch is what protects the rear bumper, and also makes enough clearance that I do not break the sewer pipes. I have to use 4WD low range. Low range so that I can tow very slowly. 4WD because I am driving up and out of the creek bed, with wet tires, on rocks and gravel.
Not everyone goes where I go. Besides all of the conditions mentioned above, many people seem to be very reluctant to tow for 3.4 miles on a winding single lane dirt road. I drive the lead vehicle towing. My wife follows in the other truck, also towing. She's a real trooper.
On edit, here is some snow data for the Donner Summit area:
Top Three 24-hour Snowstorms at the Central Sierra Snow Laboratory
February 3, 1989 — 52 inches
October 21, 1967 — 46.5 inches
February 19, 1980 — 46.1 inches
Top Five Maximum Snow Depths at the Central Sierra Snow Laboratory 7
When the snowfall will be 40+ inches in 24 hours, the plows have a hard time keeping up with the rate of fall.
1952 — 311 inches (26.0 feet)
1969 — 242 inches (20.2 feet)
1971 — 240 inches (20 feet)
1958 — 210 inches (17.5 feet)
2011 — 207 inches (17.2 feet)