From 68 to 145. I think it's not all about the tempo. The perfect tempo depends on other elements in the song. Like scrapheaper said, if it's too fast, slow it down, if it's too slow, speed it up. You can of course use TapTempo or some other software and take the same tempo that's in your favourite trap song.
For trap beats I usually use 72-80 and for the bay area/compton style beats 88-105.
It varies on how you actually line up the notes thats why so many people are saying numbers greater than 110.
The way I line up my elements, putting it at 120+ would be way too fast for almost any type of music