Rear brake disc diameter !!!

[MSPORTBMW]

Hi....im currently looking at buying front and rear brake pads for my 2009 E70 3.0D MSPORT X5.

When i enquired at euro car parts, they asked me what my rear brake diameter was !!!!

Well i aint got a clue......do they normally ask this?

All i know is i have 19" wheels with the 285 tyres on the rear.

Im looking at the brembo pads....are they a good choice?

Any advise please guys

[X5Sport]

The brakes are different diameter depending upon engine/turbo combination.  And I can't remember which size, but the twin turbo are larger as are the 4.4V8 turbo versions.