According to Official Guinness Records,
The longest ramp-to-ramp back flip on a motorcycle is 39.49 m (129 ft 7 in) by Cameron Sinclair (Australia) at the Crusty Demons Night of World Records at Calder Park Raceway in Melbourne, Victoria, Australia, on 29 March 2008.
For a complete list of 2008 records, please visit 2008 Guinness Records in Australia.