AWD question....
 

This is my first AWD vehicle. Never had a 4X4 either. Whats the difference?
I know some 4X4s have lock out hubs and some don't.
Is AWD like a 4X4? .....meaning.....if I am in mud or sand would all 4 wheels be turning at once or
is there a limited slip type setup like most 2 wheel drive cars have?

Thanks from a AWD newbie. :stickpoke

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Hello, AWD and 4x4 are a bit different. Every car maker has different AWD systems when it comes to their cars: Xdrive, Quattro, 4matic, ect. The AWD system in your 2002 x5 is a standard full time AWD meaning it has a constant 38%Front/62%Rear torque split I believe, both front and rear differentials are open with no limited slip, and the transfer case is also open, non lockable.

4x4 systems generally give you an option to go 2wd or 4wd and offer low gear and locking differentials and transfer cases. 4x4 is great for going off road or going through mountains of snow. AWD systems are more suited for slightly less off road activities. But don't get me wrong, Our X5's can still plow through snow and mud with the right set of tires.

And to answer your stuck in mud question, both 4x4 and AWD will have 4 wheels spinning, the AWD will have varying speeds on all 4 tires depending on the amount of traction, while the 4x4 system can lock all wheels to spin at the same speed.
Hope that helps!

A further clarification on the AWD system found in the E53:

The vehicle is equipped with traction control (TC), as part of the Dynamic Stability Control (DSC) system. This system senses wheel slip from the ABS sensors, and if there is a sufficient difference left to right, or front to rear, it applies a wheel brake on the spinning wheel.

While the differentials are open, this system mimics the functionality of a limited slip, but through a different mechanism.

TC is always on. When you push the DSC or 4x4 button (labelling varies by model) it turns off DSC, which is worrying about lateral stability (sliding), but leaves TC on (worrying about fore/aft traction), with different settings. What this means in practice is that TC is still there, but will intervene later (allowing some wheel slip) and the throttle pedal will not be overridden by the system. When you are spinning a wheel in the snow with DSC on, it will reduce the throttle setting, eventually to idle. That can stop you from getting out of a snow bank in the rare occasion that you want to 'churn' your way out, spinning wheels. Turn off DSC, get out of the snowbank, and then turn DSC back on to get the benefit of it on slippery roads.

Most 4WD suvs out there are usually just an open front diff and rear diff. This means even when in 4wd mode if you put a tire in the air on the rear axle and one in the front, you wont go anywhere. More recent trucks that have stability and traction etc, can turn those diffs into "limited slip" by applying some brake force on the other wheel.

Or you also have ones that come with a limited slip rear axle and open front diff, the limited slip rear helps a little.

Then you have the range rovers and i believe some jeeps, and probably a few other higher end suvs that youd never take on more then a dirt road anyways..

They have true 4wd ability where you have electric lockers for the front and rear diff, so back to scenerio where the 4wd truck with two open diffs and a tire in air on both front+rear axle wont move, this one will plow thru that since both left and right wheel on axle turn at same speed regardless.

If you have low traction on all four wheels, in theory they could all spin but in practice they won't. There will be some difference between left and right, or front to back due to varying traction. Then the TC system will apply a brake to the faster spinning wheel. If the system can not balance the wheel speeds by applying a brake, then it backs off the throttle and you won't be able to go above idle (unless you turn DSC off, which just leaves TC on)

But if you punch it in sand to spin wheels, you will likely just bury it to the axles anyway.

:iagree:
I did that with a 1978 Chevy Blazer with a locking rear differential and locking transfer case! Rather embarrassing to say the least. Fort Lauderdale sand (white and powdery) is nothing like Daytona sand (brown, damp & hard packed).

2002 X5 3.0 264,300 miles
2004 325i 116,000 miles