What speed does the DeLorean in "Back to the Future" need to reach for time travel?

The DeLorean needs to hit exactly 88 miles per hour to activate the flux capacitor and travel through time. Bob Gale and Robert Zemeckis picked this number because it was fast enough to be considered a real feat without making Doc seem even crazier, plus it looked cool and was easy to remember. The filmmakers had to get creative with the car's speedometer because Jimmy Carter had signed a law in 1979 that capped speedometers at 85 mph, supposedly to discourage speeding. So the movie's DeLorean got custom gauges that could actually display that magic number.