The method of cleaning depends upon if the clearcoat is present or not.
Or if they have been altered such as powdercoated, painted etc.
Assuming stock with clearcoat intact you don't want to use acid cleaners that can go right down to the metal.
If they are dirty and no clearcoat is left or its flaked up, I'd use an acid cleaner or bead blast them and then paint/clear coat them, or get them powdercoated.