Just got a bottle of P21S Wheel Cleaner. All the german car makers recommend this product for keeping your rims looking new. It has no acids, and therefore not harmful to the clearcoat.
Let me tell you .... this stuff work. The moment the liquid hits the rim, you can see the brake dust 'dissolve' and start running down. No rubbing required. As the instructions say... spray liberally and hose off. But if you're a perfectionist like me, you can use a clean sponge/cloth to get into all the tight areas before rinsing.
Cuts the time of keeping your rims clean in half. I usually spray it on before running my car through the Hand Wash. The wheel cleaner they use doesn't work as well.