BXT- the next phase of the Westchester South County Trailway should bring it down to Van Cortlandt- it's planned, but I don't know what their time frame is for actually building it. Once it's done, that will make getting to Sprain a piece of cake.
For those looking for an adventure, there is a back entrance to Sprain. From Sprain Road, West of I-95, North of Tuckahoe road, look for a break in the fence with a trail that leads to an old, abandoned overpass/exit. At the East end of the overpass, you'll have to shoulder the bike and climb over a railing. Once off, you'll see a guard house- if you ride into the trees across the grass to the left, you'll find a rocky, overgrown fireroad that runs the length of Sprain Ridge Park.
Sprain is ten times more interesting than Graham, IMO. Maybe it's just my fondness for rocks, drops and technical trails, but I'd much rather ride Sprain that Graham. However, it's a pain in the ass to get to Sprain without a car, so I only tend to go when someone's driving.
Jamie