I did the Dayton Cycle Club's Covered Bridge Tour a few years ago. It's only $5.00 and is a no-frills ride. I liked it.
ROUTES: 23 miles (2 covered bridges), 45 miles (5 covered bridges), 74 miles (7 covered bridges), 105 miles (11 covered bridges). Rolling to hilly terrain. Route direction arrows are marked (painted on roads) at intersections.
I want to do this ride next year: Red River Rally near Slade KY. Hosted by the Bluegrass Cycling Club in Lexington, KY. Local riders have liked their Horsey Hundred ride, too.
Here's a 2012 Red River Rally gps recording of the Sunday 65 mile route. Click the Terrain option on the Map pulldown at the top right of the page, then zoom all the way in.
The Little Miami Bike Trail isn't busy at all, except for 5 miles near the Loveland and Xenia stops. The best section is from Spring Valley to Loveland. The trail south from Loveland to Cincinnati is scenic, but can be crowded, and bumpy from tree roots under the trail.
Here's a ridewithgps map: 84 miles from Xenia to Loveland and back. Or start at Spring Valley for 70 miles, or Corwin for 60 miles.
You will need to slow down near rest stops if there are walkers or kid bikes on the trail. Otherwise, it's full speed ahead and few road crossings.