There are some good places here, along with one bad one.
Touring the historic section of Mckinney provides about 5 miles of low traffic and well kept older homes.
From downtown, taking Kentucky south to Graham, then to College picks up a bike trail around Town Lake.
From there are about 3-4 miles of quiet low traffic neighborhood roads that include a trip through a natural area near Elorado Golf course, crossing under a viaduct at Eldorado, eventually reaching the trail crossing Highlands Drive. Take that trail up to the end near the Gabe Nesbitt baseball field. The return route can be the same although there are number of really nice low traffic neighborhoods to get back to downtown. The locals will know their way so if you aren't familiar with the area it may be best to start from someone's house and all of us meet somewhere.
Open the google link and under the MAP button turn on the Bicycle option.
http://g.co/maps/n2986