Hi, During my student coarse aeroplane building i got some info on aerodynamics. the thing with cigar-shaped objects is that they tend to turn sideways. its easy to understand, visualise a cigar shaped object moving lengthwise through air. the air stops at the tip and creates statical air pressure. this is also the case at the back of the cigar where there is a similar pressure. when the cigar turns a bit at an angle to the airstream, the pressure area at the front and backend will shift accordingly, creating a moment on the body, trying to turn it even more. thats the problem with which those hpv people have to deal in these streamlined hulls. the obvious solution there is to add a tailfinn, which will create a correcting moment to the destabilising moment from the cigar shaped object described before. in case of the python bikes, there is not directly such an obvious solution. here the destabilising moment works directly on the steering front, so a fin on the back of the bike would do no good. maybe some vertical fin in front of the bike, steering in the counter direction of the pivot, to get some correcting moment on the frontpart at high speeds, compensating aerodynamic forces. one could do that with some wires attached to the backend, in their turn attached to the fin so it counterturns slightly more than the center pivot. its of absolutely no use to use a backfin on the back part. 1. it will be in the turbulence of the rider, thus rendering it useless. 2. stabalising the back of the bike will probably even make things worse, as the front wants to turn and the back dont. i could think of other solutions like extending the front part of the bike, over the riders head to the back, behind the pivot point. (like a stiff fishing rod with a vertical fin attached) that would also work, as log as the backfin doesnt get caughtup in the riders drag. //Dirk Jan