Generally, mountain biking presumes off-road action. But in the Adirondacks, some of our roads are challenging enough! Of course, with all the wilderness we have, there is plenty of traditional trail-tearing to do also. The folks in charge of wilderness policy have set some pretty stringent limits (for good cause), but what they have kept open amounts to the largest state-owned off-road biking region in NY if not the world. With the addition of the private lands that are open to traffic, you could enjoy some monster trips in these mountains.
Currently, information is hard to come by. The best reference is the book Adirondack Park Mountain Bike Preliminary Trail & Route Listing, published jointly by the ADK and ANCA. For tours on private land, your best bet is to Hire a Guide who can accompany you on your trip or get you steering in the right direction. Several Outfitters rent all the necessary equipment at very affordable prices.
As with any fast-paced activity, keep in mind that here in the Daks you can get very deep in the woods, so any major crash & burn could leave you outside all night. Make some preparations for the unexpected. Always tell someone back home where you're going, when you should get back, and anything else that may help pull your battered body out of the woods before exposure does you in. Carry basic repair kits for your bike & yourself. Bring a headlamp.
Be prepared for undocumented detours from blowdowns, fresh beaver dams, or recent logging. Don't however, lose sight of the trail. If you must detour, make sure you can find where you left the path before you wander far. Be very cautious if you must leave a trail. Look out for screened ledges- cliffs obscured by thick brush at their verge. Make certain the trail you regain is the right one! A compass will help you do this if you know how to use it. Carry a map & familiarize yourself with each turn and junction of your intended route. Know where each side trail goes.
Once you are properly equipped mentally & materially, go spin your wheels: get outta here!