From Campolongo you mast follow the road to Forcella Lavardet. This is a no tarmac road but it is wanderfull. Ignore the forbidden signals. Most bike can ride this part of road but off road or enduro bikes are better. After Forcella Lavardet head to Sauris where you have to try the local ham, the road is no more off road but a very good and new tarmac. After Sauris Lake there are two roads to Ampezzo, I suggest to follow that one that starts after the lake, you have to take a short tunnel.
Have a nice and safe ride.
Alex da Tai