Regular cleaning will help keep them wheels clean
So you have a Mercedes, or other european, or high performance car but the wheels are always dirty. The reason is the high carbon content in the brake pads mixing with dirt and grime you've picked up off the road especially in wet weather driving. We can't control the weather, and changing the brake pads can effect the braking performance of our vehicle. We can only regularly clean our wheels.Here's a tip on how I clean them so they at least look clean to start with.
So here we are before
and after
In this shot I've included all the items I use to clean wheels. They include a Oates plain rectangular sponge, an Oates Eager Beaver pad (cut in half) and some rubber gloves available from safety shops, or use normal dish-washing latex gloves) to keep my hands clean so when i clean the interior i don't "redistribute" the filth off the wheels into the car.
These I keep in a separate bucket from the items I use to clean the body and interior of the car. That way you are not transferring all the grit and grime onto the car body or into the interior. All you need now is a heavy duty car shampoo, and some OOMPH non caustic degreaser (from Bunnings).
So first I squirt some of the heavy duty car shampoo into the bucket (after removing the other items) and half full the bucket with water. Bung the sponge in the bucket and your ready to go.
Spay the wheel first to wet it, then spay the OOMPH directly onto the wheel and tyre. Then using the sponge gently wipe the wheel and tyre to remove the grime. I usually start with the tyre, then the external surface of the wheel, including the spokes.
Next I reach inside the wheel (this is where the gloves come in handy) with the sponge and clean the inside if the rim, then the inside of the spokes. These two surfaces collect the grime as well as that you see on the outside of the rim and readily spread their filth when it rains! Next use the eager beaver pad to clean any surfaces you couldn't get to with the sponge such as narrow gaps between wheel spokes.
Then rinse off all the residue from cleaning the wheel, and touch up any bits you have missed. Then dry the wheel with an old chamois and move on to the next wheel.
Hope this helps. Note, if the non caustic degreaser doesn't work you may have to move up to a more powerful cleanser but I suggest you get expert help here. Happy wheel cleaning.