Board Thread:The Flash discussions/@comment-9346948-20160420004341/@comment-3423279-20160420044933

Well it probably didn't multiply his speed, probably just stacked Barry's onto Zoom's if anything.

Zoom also had a bit of a head start and Barry isn't capable of seeing what he cant... see.

Plot Reasons, or he was scared that Zoom might be able to kill the others despite his own speed.