During the Battle of Seoul, Black Widow deployed her Harley-Davidson LiveWire from the Avengers' Quinjet to pursue Ultron's truck. En route, she picked up Captain America's dropped Shield and threw it back to him as he was fighting Ultron. Ultimately, Black Widow had to abandon the Harley-Davidson LiveWire as she used it to jump into Ultron's truck while her motorcycle was demolished as it smashed into oncoming traffic.
Black Widow's motorcycle was an electric motorcycle that was capable of traveling at high speeds and was highly maneuverable. Like Captain America's motorcycle, it can fix his shield to the front of the bike.