because of the weight placement. on a VW based trike, all the weight is in the back, on top of the rear wheels. if you turn, you need to shift a lot more weigh to the front before it tips over. in that Z trike's case, the weight is ALL up near the front, if you turn it just right, it'll go over real fast. There's a reason why a lot of drag strips don't allow trikes, and why ATV trikes aren't made anymore. Maybe if you're going like 25mph all the time it's fine, but a trike built like that isn't very safe imo.