I am trying to move a Mesh of a car about, everything works perfectly except when i try and turn it though an angle of about 45deg then the movement path doesnt match the direct of the mesh.

Code:
 car.X = (float)(Math.Cos((double)car.DegToRad(car.Rotation - 90.0f))*50.0f) + car.X;
Its only happens when the cars Rotation is inbetween -0.45 and 0.45, other that it acts weirdly.