A 100% acid-free wheel cleaner that's safe for all types of wheels. Recommended by Mercedes, Porsche, BMW, Volvo, VW and Audi to remove brake dust and road grime. This is a water-based non-acidic detergent that provides great cleaning and guarantees not to damage any type of wheel. **P21S? Gel Wheel Cleaner - for wheels that tend to soil heavily due to higher braking speeds, softer brake pads or infrequent cleaning. Spray on, allow to stand up to two hours, touch stubborn spots with a sponge and rinse off with a sharp stream of water. Gel composition clings to vertical surfaces to provide increased cleaning effect.