Bikes can move up to 12" in their movement phase. A unit of bikes can charge 6" in the assault phase if it is within 6" of the enemy. In other words they move at twice the speed of troops on foot, but assault the same.
Note that certain types of bikes are able to move much faster than this. Special values for these bikes will be included in the Codex army books where they are appropriate.
Bikers are affected by terrain like vehicles, but are put out of action if they become immobilised. If bikers enter difficult terrain roll a D6 for each model. On a 2-6 the bikers steers skilfully through the hazards, on a 1 the biker hits a tree, rock or something else solid with tragic consequences and the model is removed as a casualty. No armour saves are allowed.