My Class C had some sort of similar tire blacking shine on it when I bought it. It is indeed nasty stuff and you cannot get it off. I used a number of different cleaners that remove everything. While the stuff "came off" it leaves a residue that is there permanently and prevents anything from sticking to the tire. I tried masking the tire so I could spray paint a couple of rims that needed it, and the tape would not stick.
My tire guy said the stuff is awful and it caused the rubber to check and crack, which mine did. I ended up scrapping the tires and putting an entire new set on due to the fine checking all over the sidewalls where this stuff was.
'03 Ram 2500 CTD, 5.9HO six speed std cab long bed Leer top and 2008 Bigfoot 25B21RB.. Previous, Being repaired and will be sold, is a 2008 Thor/Dutchman Freedom Spirit 180. SOLD - 2007 Winnebago View 23H Motorhome.