I use WD-40 to clean roofing tar off my tools so that might work on road tar. I also have an old can of Turtle Wax Tar and Gum remover for my autos. It's the old stuff in a metal can, not the plastic spray bottle.
Is that a chromed steel rim? It kinda looks like aluminum alloy. If so, best way to clean is with Scotch-Bright sponge and detergent. The spots in the photo may not come out completely, but you'll probably be able to fade them some.