Rear derailleur - how much space is needed?

Question

I'm building a trike with the Shimano Tourney rear derailleur. I guestimated the range of the thing to be 22cm max, though can't be positive.

I'm using 20" wheels. Will there be enough space for it to not scrape the ground at every gear-change?

Answer 1

Using a Tourney will be VERRRRY close depending on which Tourney it is. The TY-15 is a 5 speed that is OK to use with 20", and the TY-18 is for 6 speed. NO other Tourney is usable for 20".

EDIT: Nope... TY51 will not do.