Rust can be a death sentence for some types of metal. Rusting is the chemical breakdown of metal caused by its exposure to corrosive materials and oxygen. Sometimes the elements in rainwater, salt on the streets and other materials can cause rust to develop on exposed metal. Although it starts small, rust can grow quickly and eat away at the metal. It doesn't take long for rust to permanently damage the small metal components on your bike. However, if you notice rust early and treat it properly, you can effectively remove it and reduce your risk of the rust growing.
Remove existing rust by rubbing affected areas with a steel wool pad or sand paper. Rust will continue to spread once it develops on part of the metal, but eliminating the rust will temporarily spare your bike's metal from further corrosion.
Apply touch-up paint or fingernail polish to the metal if the rust has occurred where paint has chipped away. The paint will prevent air exposure and, through that, the oxidation that leads to rust.
Apply a protectant grease or WD-40 to exposed metal, such as gears, chains and brake cables. These surfaces are at a greater risk of rusting because they are exposed to the air, but greases can help control oxidation and reduce rust.