I built a rear steer ("Dymaxium" (Sp) by Buckminster Fuller) type trike, when it says (on lorax/the-hauler) 20mph max. belive it, too fast and the thing will shifting/weight steer, causing one into a over steer correction- going to a out of control condition.
Fuller and builders of the three wheel rear steer car (back in the early 30's) tried 20~? ways to try to overcome the steering problem, never did find a listing as to how they solved the problem. (One person was killed in the crash, with the press following behind.)
The best solution that I came up with _besides a 2 1/2 to 1 reduction_ was to put a spring loaded center finding cam, (over the rear wheel) that required a lot of force to climb out of the straight forward steering position.
Maybe computer steering would solve the problem. "drive by wire"?