Catrike Speeds converted to SuperSpeeds.
Here is a 700C wheel grafted onto the back of an 2003 Catrike Speed. My test rider says that it adds at least 2 mph to the trike and is much more comfortable. 
Note the similarity to the Catrike 700. It weighs 33 pounds, the same as the 700. 
My second Speed modification using a 700C wheel fit to the back of a 2006 Catrike Speed. A strong testrider is performing durability testing.