WILLIAM BYRON. #5. While the primary focus for Hendrick Motorsports is on replacing Dale Earnhardt Jr. in the #88 car, the #5 car’s seat may be available too with Kasey Kahne, the car’s current driver, struggling and losing sponsors. William Byron is the best young driver currently not in the Cup Series. He is in the mix to win this year’s Xfinity Series championship for JR Motorsports and will definitely be in the mix for a full-time ride in the Cup Series in 2018 because of it.. Hendrick Motorsports. Chevrolet