I use Simple Green on my bike and my cages. Nothing cuts through brake dust like Simple Green, and it's cheap too.

 

Spray of your choice and a soft bristle paint brush, or a toilet brush to scrub the dirt off. Then hose off thoroughly. I chromed my fatboy wheels and they are a lot easier to clean now.

 

First if you haven't changed your brake pads to Lyndalls or some other dustless brand that will help A LOT ! I use WD-40. it will soak the oil and dirt loose and leave a film that will protect the polished stuff and make the black paint shinny. Just be careful about not getting it on the brakes too much. Not good. I tried simply Green once, spent the next 3 hrs polishing the outer rings on the wheels.