title_body: What is the advantage of a stretched-X frame over a true-X or squished-X design for racing? Most racing frames on the market appear to be stretched-X (longer than they are wide). 
  
  I have heard the argument that a stretched-X allows better airflow to the rear props due to physical distance, but in a racing environment, the quads are usually flying at a much steeper pitch angle than any other form of flying which should give the rear props much cleaner air.
  
  In my experience flying line of sight, stretched-X frames seem to have more pitch authority than roll which would seem to be the opposite of what would be desirable in a racer.
  
  Other than the fact that they are a little narrower so they fit through the gates better, can anyone offer any advice as to why stretched-X frames are so popular?
upvoted_answer: I'm not a frame designer, but one distinguishing characteristic comes to mind as to why stretched-X frames are more common.
  
  As you mention, a stretched-X frame has a longer front-to-back dimension than its left-to-right dimension. In addition to providing the rear propellers with cleaner airflow when in forward or backward motion, this results in the moment of inertia about the pitch axis being higher, which means that it requires more work for an external force (e.g. wind) to change the pitch of the quad inflight.
  
   (cit.)
  
  This also means that, as you noted, the pitch axis has greater control authority (due to the longer moment arm) which allows the quad a more quickly accelerated response to the pilot's commands. The differences in control authority accessible to the pilot can be smoothed over with rate profiles and PID tuning so that the quad maintains the stability it gets from the stretched-X design while responding uniformly to pitch and roll commands.