Here's a similar map I came up with.....just for mulling over.
Day 1: The ride to Ludington, MI - I started the ride map in Lansing, although folks coming from the west could pick up the ride in Grand Rapids, Muskegon, or jump in at Ludington the next morning. I didn't think about routes to Ludington at this point (map shows interstate for part of it). Shortest route = 162 miles from Lansing (+whatever folks tack on to get there). Easy ride. If we started at noon we could make a few stops to pick up folks and get to Ludington by dinner. Apparently there are some good roads in the Ludington area (+ parks and a beach), so those could be options once we get there and perhaps on the way. There are places for die-hards to camp as well and the Manistee National Forest is close by as well.
Day 2: Around to the Mackinaw Bridge - Departs at 9am and should arrive on the other side of the lake between 12 and 1pm. This would be a good place for people from the other side to meet.
The ride could then head north into the UP via route 41 to Marinette. Then onto Route 35 into the UP and perhaps along Route 2 along the Lake to the Bridge. This would be 300 miles from the ferry. Not really a lot of riding, but it's worth considering the road and stops, and the fact that we don't really do much riding until the afternoon.... If the northern part of the UP is a better ride (and I hear that it might be, but haven't been up there....) we could try a route up through that way, which would tack on at least another 100 miles or so I think. I'd be up for that.
We don't have to ride all the way to the bridge on Day 2, although the next day is a lot of winding (slower) roads and people don't want to miss that (plus people might want to leave enough time to get home on Day 3 as well). if we get to Mackinaw City by the end of Day 2 there are lots of places to stay (it's a small tourist hell for those who haven't been there, but it's also kinda fun).
Day 3: Down Lake Michigan - Route 31 to Traverse City and then Route 22 up and around the Leelanau Penninsula and down to Manistee (taking the scenic Route 109 bypass as well as the Route 110 bypass into Manistee (the latter part is THE twistiest road I've been on in Michigan - it's awesome). From there 31 goes straight back to Ludington. I drool just thinking about these roads..... I've done a bit of them and it was all breath-taking. Only 255 miles to Ludington, but it's easily an 8-hour trip from the bridge with a few stops. Tack on another 160 miles to Lansing + whatever folks need to get home and it's plenty I think. I love the Iron Butt thing, but this probably isn't the time. Total = 940 miles Lansing to Lansing.
Here's a map....
from:Lansing, MI to:ludington to:manitowoc to:M35 to:mackinaw city to:US-31 to:M-22/N Manitou Trail to:M-22/N Manitou Trail to:M-22/W River Rd/W Western Ave to:M-109 to:M-22/Scenic Dr to:Frankfort Ave/M-22 to:6th St/M-22 to:M-22 to:44.333672,-86.2761