BMW cross bars with Thule Cascade box.

[Tipper21]

I'll be picking up my new '08 X3 in a day or so and would like to use my Thule Cascade roof box on it. The BMW base support system cross bars seem pretty thick compared to the Honda CR-V roof rack I used this box with before. Has anyone used my proposed combination? Don't care to buy the BMW bars and find my Thule won't fit.

[b-y]

I have not used the specific combination you describe, but have some experience that may be comparable. You basically have two options:

Use the BMW cross bars and special adapters to replace the Thule clamps. The factory cross bars for BMW, MBZ, VW, etc. have slots (as do Thule "aero" cross bars no longer sold in the US). But Thule (and others) make adapters that look sort of like upside-down letter T's that slide into the slots and bolt onto accessories such as the Thule boxes or ski racks.
Buy Thule cross bars that attach directly to the X3 rails.

[X3 Skier]

When I was using a Thule Box (now my short skis fit inside the car) I made a couple of brackets myself out of a length of threaded rod bent into a U shape with a neoprene sleeve over the rod to fit the x3 cross bars. Drilled holes in the bottom of the box to fit and it held up fine on several cross country trips. Even fit my wife's Jeep Grand Cherokee which has cross rails already installed.

Cheap but effective.

Cheers

[JBasham]

I had a Thule box before I bought the car, and I bought new Thule rails and clamps to fit the X3. I like them. I didn't seriously evaluate the BMW rails, though.