are only supposed to run "low" pressure on these tires when you are at the strip. When you are back on the street at speed(s) for extended periods you need to be back up at a more normal pressure (like ~ 30 psi or so). You shouldn't be using your DR's as a normal commuting tire, but I definately wouldn't recommend driving around on them at only ~ 20psi all the time.
What I do is swap them on the day of an event and drive to and from the drag strip from home.