According to Official Guinness Records,
The largest Hot Wheels loop-the-loop is 3.81 m (12 ft 6 in) and was achieved by Matt West, Blade West, John Jaranson, Grant Compton, Jeff Schoppert, James Barnabei, John Gambino, and Tim Walker (all USA) at the Ford Motor Company Research and Innovation Center in Dearborn, Michigan, USA, on 5 May 2015. The loop was set up as part of the company's 'bring your child to work' day.
For a complete list of 2015 records, please visit 2015 Guinness Records in United States.