Why are the two front wheels rims getting dirtier then the rear wheel rims? on 2009 Mercedes-Benz R350

My R350 needs a wash, but what's got me baffled is that the front wheel rims are a LOt dirtier then the rear wheel rims; my husband is concerned that it may have something to do with the brakes or brake fluid. We are still under warranty, so will take it in, but hoping I can get some good advice here first.

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2 answers
the dirt is from the brake pads. it is the result of brake pad wear. ceramic pads emit less dirt but will dirty the wheels anyway. stay on top of it by cleaning the wheels regularly.
there will be no warranty as this is normal wear and tear.

Roy
There are cleaning products like Eagle 1 to remove brake dust from the rims and other products you spray on and wash off.