That is concrete residue. Happened the night my car was hail damaged. I got it off the body using distilled white vinegar, But that does not work on the wheel wells.
Car is going up on jackstands tomorrow so I can pull the wheels off and give the undercarriage a good cleaning.
94 Firebird Formula (Drowned 08/30/05)
2010 IBM 2SS/RS 6M Arrived 3/25/10.
ADM CAI, Borla Type S Cat Back, VMAX Ported TB, LG Short Throw Shifter, Hotchkis Max Chassis Brace, BC Racing Coilovers, Hotchkis Sway Bars, Whiteline Cradle Bushings,Forgestar F14's 20x9/11,Nitto Motivos, Stainless Power Headers, Solo J Pipes, AAC LED Sidemarkers, ZL1 Rockers, SLP Splitter, ADM Stage II Cam.