I was lookin recently at some possible minibike adventures. If I head North from Davison, up M-15, zig over to M-24, and keep on truckin, I'd be into the thumb, maybe right along the coastline. It would be a, all day, big nuts, kinda ride for me. AKA...awesome.
I've been thinking along those same lines, for the last 2-3 years now. For you, just hang a right on M-15 and you can keep going at least to Vassar. Last time I went through there, it was still largely rural, the roads lightly traveled. Need to do a little recon, it's been 20 years since my last trip through the Thumb area. Given my druthers, I'd prefer a little more laid-back pace than is the norm, on M-15, south of your location. Pushing 55mph+, for 20-40 miles at a stretch, becomes tiresome after a while. Just slowing that down to 50-55mph, makes all the difference. And, I think that should be possible, just by avoiding a few of the main highways. Of course, the guys who don't have bikes capable of those speeds have to be accommodated, too...or they're excluded and we want to avoid that.
This is a well-established thread, so I really don't want to turn this into a hijack. Let's start another, dedicated, thread...in the appropriate folder...to discuss some ideas. We've months to go before riding weather returns, here. For now, suffice it to say that, imo, there are three basic possibilities: coastline, interior and small town/campground. It doesn't necessarily have to be a single day ride. There are two state park campgrounds along the Lake Huron shoreline, from which different rides could be staged.
Being in Florida, I was trying to figure out what the hell "thumb area" meant. Kirrby's response helped a bit. Do you guys have a "middle finger" area too? If you do, I'd guess it would be Detroit.
The middle finger is Lansing.