The x-drive system uses a variable clutch to change how much power goes to the front it’s a bit of a misnomer to say it can transfer full power to one axle that’s only true if the other axle has zero traction and can be dragged with the abs locking the wheels.

The pre Lci uses a pure planetary gear system that uses gear ratio to divide torque. No slipping of clutch plates and can handle any speed differential. I think that the problem with different size tires will come from dsc detecting some wheels going faster than other and using abs to attempt to correct this.

The wheels and tire sizes are very carefully selected so the rolling circumferences are almost identical if 17-18-19" wheels

Eg: 235/65/17 255/55/18 255/50/19 all have nearly identical rolling circumference so the 17 can be used as a spare.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)