well i have a cleaner for my tires and wheels, it says "dissolves brake dust and road grime", the brand name is "STREET APPEAL PROFESSIONAL", bought this from BIG baazar's dollar shop, here in Hyderabad, i once used this to clean the tar like thing that comes under the door panels used by the manufacturers to paste the plastic sheet beneath the door panel.
accidentally this tar like thing this got stuck to my doors while my new swift was getting ICED, and used this clear worked way effectively with out having any kind of effects on the car's paint!
i suggest you either go to the windshield experts or get this kind of grime dissolver and clean the salts that have deposited! its just that you need to use it in the concentrated form for cleaning the salt initially and later use lots of water to dilute it out and clean it off the surface where it was applied so that it does not react with the actual material!
i have been using it for like 2 months now and i apply it once a week on my tyres and wheels and they stay like new for the whole week!
here is a picture of the same!
Windshield Repair, Auto Glass and Auto Safety Glass Replacement Services Center India
this site should give you all the address you need on the shops near you!