Georg300 as for the 4wd thing, do you have a manual? here are a few statements.

Please look at page 187 as it explains the Four-wheel drive well. I.E. the distribution between the front and rear wheels axles is 38% to 62%. This is why the chains go on the rear.

Pg 86, DSC: In the following exceptional circumstances, it may be effective to deactivate the DSC for a short period:

-When rocking the vehicle or starting off in deep snow.
-On sandy road surfaces
-On poor surfaces with deep ruts
-If the wheels "churn" on muddy surfaces.
-When driving with snow chains.


Pg 132 winter operation:

Snow Chains: Mount BMW snow chains only on tire size 235/65 R 17. Always mount chains in pairs and on the rear wheels only. Read and comply with the chain manufacture's safety precautions. Do not exceed a maximum speed of 30mph(50km/h).

Starting off: When starting in deep snow or "rocking " the vehicle free, it may be advisable to deactivate the DSC system briefly. Refer to page 85.

Personally I would run chains on my 18" tires and have a set. I have never had to due to my snows. Now when not on snow tires the manual precautions pay off.