if those are aluminum, go to a lowes or home depot and get 2 spray bottles. then get distilled vinegar, dish soap and a soft bristled dish wand. one sprayer should have only water. the second will get a good squeeze of the dish soap, half filled with vinegar, then fill the rest with water and shake it. spray the vinegar mix on the wheel, spray your brush and use it to scrub your wheels. when your rim looks free of road and brake dirt, spray it with the water and wipe off if you want. i did it to my wheels last week and it melted the dust right off
How about you buy Meguiars All Wheel Cleaner and spray it on the wheels and let it do the work for you and than use your pressure washer to spray it away