The Ogemaw Hills Route makes for a nice ride, but is not very long. The ORV Trails are for vehicles under 50" wide, but all of the forest roads in the area are available to you as a street-licensed vehicle. That opens up a ton of miles in the area that are legal, just make sure you avoid steep hill climbs or mud that would not be passable in a conventional 2wd car.
I like the road system and routes a few miles west closer to St Helen too, along with the ORV scamble area with some nice little sandy hill climbs, some tight trails etc to play on. You will need an ORV sticker if you play in the scramble area (technically the St Helen Motorsport Area on the maps). The DNR website is not cooperating today, can't post a link to the maps - sorry.