I live in Newmarket and I'm thinking of doing a loop around lake Simcoe this summer. The part I can't quite figure out is the west side of the lake ... what roads down from Orillia to the south end of Barrie to hook into Yonge St or 10th sideroad are the most bike friendly.
Google maps leads me to think that perhaps Old barrie Rd -> 7th line -> Ridge Road might be workable ... but it's not an area I'm familiar with.
Currently I'm riding a steel flatbar bike but I'm hoping to do this trip on a new road bike. That trail looks interesting but not quite what I had in mind .. especially if I decide to go counterclockwise around the lake as I expect I'd be pretty tired by that time.
Ridge road is pretty nice for road cycling in my experience. I commute by bike on it from Oro-Medonte line 11 into downtown Barrie two or three times per week through the nicer seasons. The newly paved part from at least line 11 down to line 8, where it ends at the top of a small rise, going back to older but still decent pavement. Some parts of Ridge road, on the South-West bound side, are sketchier near the shoulder but no large pot-holes or significant hazards.
The main downside to Old Barrie Road (IMHO) is that there is a little more large-truck traffic on it, which I don't personally like. It's also hillier than ridge, with larger hills and more if them. It's very scenic though and pretty good pavement on the parts of it that I've ridden (only lines 11 to 8 on that one). On the same side of the highway but less busy than Old Barrie Road is the 15/16 sideroad which goes right past my house and I sometimes see groups of roadies on it. It will only take you from line 14 to line 3. I find the pavement on the 15/16 to be pretty cracked and crappy for my road bike though so I avoid it. I would say it's generally ok closer to Orillia, and worse closer to Barrie.
If you're looking to cross the highway on any of the lines, you should also know (just in case you don't) that they don't all have overpasses, only lines 3, 5, 7, 9, 11, 14 & 15. Not sure why it was done that way, just happy to live on one of the lines that does have one.
Once you're in Barrie the lakeshore trail or lakeshore drive connects to Yonge via Minet's Point Road, or to Burton (which becomes Yonge) via Tiffin, then Essa (maybe construction here for the old/new train station).
I've thought about circumnavigating lake Simcoe by bike someday too but haven't worked up to that league of endurance as yet.