towing with chains...

[Byron Kinnaman]

Originally Posted by Jared J

Awd can be selectable, and there were also plenty of factory full time 4x4's (ford, chevy, dodge all did with np203 t-cases), that were not selectable. Yes, some 4x4's can only have two wheels driving, limited slip can help with that, lockers or spools guarantee they all turn.

I have never seen just one wheel turning in my all wheel drive. I've seen one quit momentarily, and that's it. The entire point of awd is that one wheel ISN'T the only one powering the car.

As for chains, if you need them on the tow vehicle, you need them on the trailer.

I realize this thread isn't a discussion on the mechanics of Awd and 4WD. But I do have a question for you. In the case of full time AWD how is the difference in wheel speed managed on dry pavement? For 2 wheel drive the differential manages it. But AWD and 4WD hmmm??

[Jared J]

Originally Posted by Byron Kinnaman

I realize this thread isn't a discussion on the mechanics of Awd and 4WD. But I do have a question for you. In the case of full time AWD how is the difference in wheel speed managed on dry pavement? For 2 wheel drive the differential manages it. But AWD and 4WD hmmm??

Center differential.

[Jon Vermilye]

As I understand my RAV4, there is a fluid coupling between the front & rear drive train. The reason they require replacing all 4 tires at the same time & chains (if used) on both front & back even though most of the time it is a front wheel drive vehicle (over 25 MPH) is the fluid coupling will overheat if the speeds between the front & back are different for too long. I could be wrong!

[Brian B-P]

Originally Posted by Byron Kinnaman

I realize this thread isn't a discussion on the mechanics of Awd and 4WD. But I do have a question for you. In the case of full time AWD how is the difference in wheel speed managed on dry pavement? For 2 wheel drive the differential manages it. But AWD and 4WD hmmm??

Originally Posted by Jared J

Center differential.

Yes, a centre differential,
or
direct drive to one end and drive through a clutch to the other. The direct (always driven) end is typically the only one which is driven in the 2WD version of the same vehicle. The clutch can be a viscous coupling, or a mechanical plate clutch hydraulically or electrically controlled to slip as much as necessary. Most slipping-clutch systems completely disengage the not-always-driven end under normal conditions, but under challenging conditions with a front/rear tire diameter difference may slip continuously and have wear or heating problems.

I don't think there are many centre differential systems left, although there are some.

The oddball exception is the Toyota Highlander Hybrid (and anything else following the same "4WD-i" design), which drives the front wheels all the time through the usual Synergy Hybrid Drive transmission, and drives the rear as needed by an electric motor. Because there is no mechanical link between front and rear axles, it shouldn't care about a tire diameter difference (including due to chains) except that the system could be misled into thinking the fronts are slipping and thus drive the rear excessively. This system is not intended to drive the rear all the time, and the rear drive unit can overheat if driven too hard for too long. I would check the manual or with the manufacturer of any vehicle before using chains, but especially with this electric system

[Jared J]

Sorry, I misread. No thought he asked about the full time 4x4.

My awd uses a viscous coupling, I believe.

[Raz]

Originally Posted by cpaharley2008

Here is a site for some applications and accessories like this
Snow Tire Chains Ramp

Save your money. To install chains, one side at a time, place the non hook end over the top of the tire as if it were installed. Tie the end loops together with a piece of rope through the wheel. Slowly drive forward. The chains will caterpillar around the wheel. You want to stop when the rope has emerged behind the wheel. Now connect the hooks. I use wire ties to tie in any loose chain to avoid damage. Practice it once and you'll see how easy it is.

Next to chains the best thing you can have is a good set of radial snow tires with lots of sipes. Michelin x- ice, Glisaved, Hakkapeliitta, etc. Freezing rain and "snot" snow (step on it and it turns to ice) are the worst. That's when the town road crews put on the chains. The colder the snow, the better the traction. Stay safe. Raz

[SilverGhost]

Point 1) 4WD is user selectable, AWD is not. Now there are many variations with good and bad points.

Point 2) Read the owner's manual or google search. Some systems can be damaged by only installing traction aids on one axle or even the wrong axle.

Point 3) If its bad enough to need "chains" put on the they should be on at least on axle of each vehicle.

One thought to consider - if you start to slide and jack knife how are you going to apply the trailer brakes without it coming loose as well?

Jason

[Brian B-P]

Our vehicles have four wheels, so "all wheels" means the same thing as "four wheels", so fundamentally AWD=4WD=4X4... and there are lots of ways to implement that, with lots of associated marketing terms. Now, if you have tandem rear axles then AWD is 6WD / 6X6, but then we're not talking about tugs for lightweight moulded fiberglass travel trailers

Originally Posted by SilverGhost

Point 1) 4WD is user selectable, AWD is not.

If only the terminology were that consistent... but it's not. You can't depend on any such simple scheme. For instance, Toyota at one point sold the very same system in the Sienna as "AWD" and in the Highlander as "4WD"; this Highlander and other vehicles have had systems with no possibility of driver selection, labelled as "4WD".

That makes this very important:

Originally Posted by SilverGhost

Point 2) Read the owner's manual...

Absolutely!
... especially if you are considering tire chains.

[Jared J]

Subaru has has user selectable all wheel drive.

To me and everyone I know in the offroad segment, 4x4 means that if it is controlled at all, the system provides power to it all (yes, the differential can transfer it) and that's that.

Awd is controlled vja mechanical and/or computerized means to shuttle traction around to tires that can use it.

Yes, some manufacturers have started muddying the terms lately to make their setups sound good, but that's my take on it.