Is 4x4 really 4x4??

[xterrasesc]

Read in an article that when you have the X in 4x4H, it was recommended that you do not drive itin 4x4 on DRY roads, is that true? They state that if you did try to drive in 4x4 mode on DRY roads and try to steer, it's very difficult.. any reasoning to this??

Thanks for your replies!

xterrasesc

[DeFibVT]

If you leave it 4HI on dry pavement and turn you cause binding of the drivetrain. The front drivetrain of this 4x4 vehicle does not have a differential unlike AWD vehicles who do. The differential allows the outside wheel turn faster and the inside wheel to turn slower in a turn. Without the differential the drivetrain will bind when on DRY pavement because both wheels are turning at the same speed.

I hope this is clear if not I am sure others will chime in with a better explanation.

[Schludwiller]

Originally posted by DeFibVT
I hope this is clear if not I am sure others will chime in with a better explanation.

I thought that was a great explanation. The only thing I would add is that on a gravel or slick road the tires can release the tension caused by the binding. They cannot do this on dry roads, thus the warning.

[DeFibVT]

Thanks Schlud, I just tried to make it simple. If I got to technical I would screw it up.

[OffroadX]

Originally posted by DeFibVT
If you leave it 4HI on dry pavement and turn you cause binding of the drivetrain. The front drivetrain of this 4x4 vehicle does not have a differential unlike AWD vehicles who do. The differential allows the outside wheel turn faster and the inside wheel to turn slower in a turn. Without the differential the drivetrain will bind when on DRY pavement because both wheels are turning at the same speed.

I hope this is clear if not I am sure others will chime in with a better explanation.

Actually, you did screw it up The "front" drivetrain does indeed have a differential, as do all vehicles where the front wheels are driven, be it FWD, 4WD, or AWD. The axle differentials are what allow the inside and outside wheels to turn at different rates, be it the front or the rear. Non-driven wheels (like the rear of FWD vehicles) don't need them since they are islands unto themselves and are not connected to each other.

What the Xterra doesn't have that AWD and full-time 4WD vehicles have is a center differential. In a turn in 4WD, the front wheels are able to distribute the difference in rotational speed between themselves via the front differential, and the rear wheels do the same via the rear differential. However, the net distance travelled by the front wheels is more than the rear wheels, and this leads to a need for a center differential to allow the front and rear halves of the driveline to do so.
Without a center diff, this stress is released by one of the wheels rotating faster or slower than it ordinarily would and skidding a small amount, provided the traction available is low enough to allow the tire to break traction. If there is too much traction, the difference in rotation builds up to a level (called binding) that can break parts of the driveline like hubs, CV joints, u-joints, gears, etc. before the tire can break traction and relieve the stress.

So, if there is adequate traction, stay out of 4WD in a part-time system or risk driveline damage.

Brent

[DeFibVT]

No reason to be sad Brent . Thanks for clearing it up.

[xterrasesc]

Thank - you to all that have replied.. Totally makes sense...
Isn't this kind of a drawback then? i mean it's not 'full time' 4WD.. DO you guys think that Nissan will add a Center Diff in the future?

P.S. let's be happy people! =)

[rrdstarr]

You might see AWD on the Pathfinder, but doubtful on the X. Remember it's supposed to be an "affordable" vehicle?

See that's what I'm talking about!

Answers with no hassle. I wondered the same thing because I read the same 4WD HI statement but I knew that unless somebody else asked it I'd get no answers.

Thanks Brent!

A related question:

So is it safe to drive regular roadway speeds if you are in 4WD as long as the road is straight?

A couple weekends ago I drove up (up, down, zig-zag) to Winter Park (scariest drive in Colorado!) and I was in 4WD for the zig-zag part up and down the mointain, but when I got to the sections of straight, mostly cleared road I would pull over to the shoulder and shifted out of 4WD HI (ala the 4WD pavemwnt question) because I wasn't sure if the thing would explode at 60mph. Did I have to do this? Or is it safe to drive on dry pavement at 55mph as long as its in a straight line?

[Goliath the X]

4-LO is limited to 30 mph because of the reduced gear ratio. 4-HI, iirc, is the same gear ratio as 2-WD. (read your drivers side sun visor sticker)

4-WD, HI or LO, is for low traction situations, so are slower speeds.

Speaking of that damn sticker. Does anyone know how to get that thing off without damaging the head liner?

[rrdstarr]

Were you driving on snow in 4Hi? I sure hope so otherwise you'll tear up your running gear! Think about this, do you really want to go 50mph in the snow on a treacherous road? I won't go above 35 in 4Hi, but that is me. I grew up in western MT driving in snow for five months of the year and learned when you do and don't need 4WD.

[OffroadX]

If the pavement is dry, or even just wet, put it in 2Hi even when it is straight. You're getting no benefit and sucking extra gas.
More importanly, if you have a tire go down on you it will cause the same binding to happen.

Brent

[Kerensky97]

Originally posted by Sham365
[Bbut when I got to the sections of straight, mostly cleared road I would pull over to the shoulder and shifted out of 4WD HI (ala the 4WD pavemwnt question) because I wasn't sure if the thing would explode at 60mph. Did I have to do this? Or is it safe to drive on dry pavement at 55mph as long as its in a straight line? [/b]

You can shift from 2WD to 4HI at any speed once the hubs are locked.

I usually drive 35 MPH on the snow pack but then hit a patch of pavement and speed up to 55 MPH , just shift the lever to 2WD.
Once I get to more snow I slow down and flip back to 4HI.

The transfer case won't disengage 4WD untill you relieve the stress on the drivetrain, you can do this by coasting for a few seconds.
Just don't be worried because the 4WD light doesn't immediately go off.

[warmonger]

Kerensky,

That is the benefit of "Shift on the Fly", or a synchronized transfer case. In the old days, transfer cases used gears to engage and disengage the front drivetrain with no synchronization. With the introduction of chains on the full-time units in the mid-70s 4WD trucks came the ability to synchronize the 4WD engagement. Now you can shift in and out of 4WD at will, even with manual locking hubs on an X. Simply lock the hubs and drive with them that way. Then when you need 4WD, shift into hi and keep on truckin'.

AWD is a totally different animal. As has already been discussed, it uses a differential in the transfer case. This serves two purposes, first it allows the vehicle to steer easier on turns, although on sharp turns it still binds up, at least on the new GM systems. Subarus don't seem to have much problem with it.

Second it allows the torque to be split as needed. Using a system of clutches, it allows slippage from front to rear in much the same way a limited slip diff works. It can transfer torque from front to rear as needed. Some AWDs (Ford Exploder and older Land Rovers come immediately to mind) have a diff lockout in the transfer case that locks the front and rearend together to eliminate the clutch pack and act as a normal transfer case.

Now are you confused?