Cupra 290 Multi Black Alloys, Try this, works for me, no sratches to date. Wash thoroughly and carefully with a hose to loosen all the dirt, do not use a pressure washer. Repeat if necessary. Leave for a few minutes and apply Bilberry Wheel Cleaner, with a spray gun, neat or mixed with clean water to your level of dirt to be removed, great smell, non acidic. Wait about 5 minutes, do not let it dry out though, wash off with a hose, not a pressure washer. If all the dirt and brake dust is not removed repeat the exercise. Aggitate with a clean paint brush and clean off.