Shamrock- the tandem just felt "wrong" to me for about the first 1,000 miles. Then it felt okay. There may be more flex on some frames than on others (like old cruiser tandems, for example.) A heavier taller stoker would make stuff like that more noticeable. On turns, your stoker shouldn't do anything, she doesn't need to lean or anything, otherwise, it'll be moving the bike when you're not expecting it to move. You do need to turn wider. Avoid U-turns until you're comfortable with the bike, and even then, it'll be a lot wider turn than a single bike, and wider than a tandem without the stoker. My stokers so far have never minded hopping off the bike to flip it around if that avoided a risky U-turn.