Here's a good loop to try in the North Hills, going past both sides of Hartwood Acres. The author describes it as a "nice scenic low traffic/ good road route, and can be varied between 25 to 70 miles, depending on where you cut off." (Note that this is not the quickest way to Hartwood Acres; it just goes by it. For the most direct route to Hartwood Acres, see "audubon".) Here's his description, with a few edits and corrections:
Escape from Pgh via the Fleming (62nd St.) Bridge. (See the "Bridges" file if you're uncertain how to do this.) Go north on route 8, either straight along the Etna bypass, or by cutting down into town and joining route 8 north of Etna (as described in the "Bridges" file). The Route 8 section has the worst traffic of the entire ride, but it only runs about a mile (or less, depending on where you get on).
Head north on Rt. 8 to the intersection with Saxonburg Blvd/Middle Rd. Turn right, then left to get on Middle Rd.
Keep going on Middle Rd. as far as you want. It starts with a long gradual rise (Vol. Fire Dept. at top), then back down the otherside of the ridge. From then on it's rolling hills. Beware that at the end of the first drop, there's an intersection (don't go flying through it!). You'll pass by the west side of Hartwood Acres.
A good cut off for ~35 mile trip is the Yellow Belt. Take a right, and follow it awhile, as it merges onto route 910. After you cross the Turnpike, there's a good short killer hill. Turn right on Saxonburg Blvd. You'll pass by the main (east) entrance to Hartwood Acres - a nice place to stop for lunch. There's often a fruit/veg stand around the corner, just before the park.
Take Saxonburg Blvd to the Green Belt (Hart's Run). Left on Green Belt. Now follow the Green Belt all the way back to the river (lots of turns and wanderings through Fox Chappel, but well marked). Ice Cream at Isley's (or the new Dave and Andy's). Right on Freeport Rd. About 1 mile to Highland Park Br. (Careful! Dangerous bridge - don't walk on the sidewalks!). Exit bridge from left lane. Right on Washington Blvd, and return home.
That's it. A nice ride, and you can vary the cut off between Middle Rd and Saxonburg Blvd, they both head north for a long way. (But don't try Cedar Rd (early on, just past Hartwood) - it's not paved).