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Nitpick time: A right triangle is any one that has one 90-degree angle. An isoceles triangle is any one that has two equal sides. (Equivalently, a triangle that has two equal angles in it.) There is exactly one that is both; it has a 90-degree corner and two 45-degree ones. For a trike, you would only consider isoceles triangles unless one front wheel is to be forward of the other.
That out of the way:
A general rule of thumb is when you widen the track at one end of the car, you get better lateral grip, and when you narrow it you get worse. This has to do with a lot of factors, but it holds pretty true in most cases. So a narrower rear end will tend to promote oversteer, which can be fun but can also be hazardous.
Going to a single rear wheel can make for exciting situations if you have a good amount of torque and drive anywhere that they paint the roads, or water gets on them, or other contaminants get on them. A friend found that out the hard way with his Corben Sparrow; on a rainy day he tried to turn and accelerate at a cross-walk. The rear tire spun pretty much instantly, throwing the car completely sideways. He said that it was just barely controllable and only because of his autoXing experience, and if the road had been any narrower he probably would have slid into a curb. Which can easily lead to a roll-over.
If there had been two drive wheels with a differential between them, only the low-traction wheel would have "lit up", and he would have pretty much just been sitting still, spinning one wheel.
All of this stuff can be mitigated to some extent by making various trade-offs. Some of it also won't be a factor under everyday driving conditions, but sometimes you hit extra-ordinary conditions.
There are enough things going on that experimentation is really the only way you will find how a given setup is going to drive.
-soD
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