The "tadpole" configuration
Simply means a trike with two wheels in the front. From what I have read, the tadpole bikes tend to be very maneuverable. Being low to the ground makes them fast, but harder to see than a regular bicycle. Going up hills in a tadpole usually causes a slight side-to-side movement with cranking which I suspect is where the name came from.
A hard-shell tadpole example would be the Go One velomobile. These HPVs look really sharp, go fast, and with electric assist approach the convenience of a small automobile. However, at almost 14K, the Go-One is a bit pricey. A less expensive soft-shell example is the "velo Kit". Not quite as "cool" looking, but it probably does do the job of keeping the driver out of the rain and may provide some wind reduction all for significantly less money.The "Delta" configuration - A trike with two wheels in the rear.
Delta trikes can have some significant advantages. They tend to put the rider high in traffic and can have high ground clearance (although this depends on the model of trike). However, there is an unpleasant choice with two wheels in the back. Having a solid axle would be a performance problem going around turns since one wheel would want to spin faster than the other. Having one wheel powered while the other isn't would make the bike inexpensive but it would cause a pull to one side going up hills. Having a differential would solve both problems but differential gearing adds to the cost. Delta bikes tend to be seen more easily in traffic but they can be more susceptible to wind issues, drag issues and turn instability at higher speeds. A good winter trike example would be the RainShadow kit that was developed by Lightfoot Cycles. This project was apparently an experiment and is not available for purchase. I suspect this is due to feature escalation making for a high cost bike that doesn't look very stylish. With electric assist, this model can also blur the line between unregulated HPVs and larger motor vehicles that are regulated.
