The Flevo is certainly an extensible concept bike: here a novel passenger trike seen in the factory in September of 1992. I'm not sure how well it rides, but any mass in the back of it must help to stabilize it on course. Then again, it takes a special kind  of rider to master it in the first place. Observe that, unlike the Chinkara, the Flevo is built up of square, straight- section tubes. But the FWD principle remains the same. Because of the large mass of the swinging front, a parked Flevotrike must be leaned against some support, or else it will fall over  under its own weight.