Can anyone help me identify what set this bag with grey and dark red pieces belongs to?
As the comments said: it's hard to tell. 

But based on

Plate 2x14 in light buish gray, 

Slope, Curved 10x1 in light buish gray and 

Slope, Curved 3x1 No Studs in  Dark Red 

i believe it is bag 2 from 

75012 BARC Speeder with Sidecar