Originally Posted by S-Dot
That's what understeer is - the tires slipping on the pavement. If they're not slipping, it's not understeering; it's just steering. When traction is lost, the system detects the difference in the rotational speed of the wheels and redirects power accordingly.
Assuming for purposes of discussion your concept of understeer is both accurate and complete, xDrive does not, and cannot, do anything to the front wheels other than to decrease the amount of power transferred to them.
That is, xDrive can only address the loss of traction induced by xDrive transferring too much power to the front wheels in the first place.
Ironic, at best. It is not coincidental that the best handling is achieved by not
transferring power to the front wheels in the first place.
By your logic, an AWD vehicle would thus exhibit a percentage of understeer based on the proportion of their front wheel drive power, and a percentage of understeer resistance based on their rear-wheel drive power? And the net effect of this is what? A hole in the space-time continuum?
No, but very cute.
The problem with AWD and turning: any front tire traction used to propel the car forward cannot be used to turn the car. This inherently decreases the ability of the car to turn. With RWD, all
of the front wheel traction is available to turn, one of the reasons RWD handles better (there is also AWD torque steer, weight differences, etc.)
This relative unwillingness of an xDrive car to turn is easily felt in day to day driving. A car using only 50% of its capability to turn feels very different than a car using 85% of its ability in the exact same turn. This is why a sports car feels much more comfortable than a sedan in a corner; it is working much less hard. This is one significant difference between RWD and xDrive.
xDrive is great for increased traction in snow and on ice while going in a straight line. This ability has its costs. Only the individual buyer can determine whether the compromise is worth it. This is a perfectly valid choice.