Why is there Black grease on your car rims?

Black grease or dust on car rims its a brake dust the style of brake pad is primarily to blame

The 2 most common pad types that cause this problem are organic or semi-metallic.

Non-Asbestos Organic

This type of brake pad, commonly referred to as NAO, is made from organic materials such as fiber, glass, rubber and even Kevlar. These types of pads are usually softer and don't create much noise, but they tend to wear faster and create a lot of dust.

Low-Metallic NAO

These are made primarily from an organic formula mixture with small amounts of copper or steel added to help with heat transfer and provide better braking. Because of the added metal, there is usually a considerable amount of brake dust and these pads are often noisy.

Ceramic Brake Pads

Ceramic brake pads are composed primarily of ceramic fibers and other filler materials. While ceramic brake pads are usually more expensive than other types of pads, they are cleaner and produce much lower noise levels. Also, they provide for Excellent braking and don't cause a lot of wear on the brake rotors.

Replacing regular brake pads with ceramic brake pads, like a NiBK ceramic dust less brake pads will eliminate the appearance of heavy black dust on the rims.