Sinclair, of Melbourne, nailed the trick at the opening show of the Crusty Demons' New Zealand tour, which reaches Dunedin on February 7, the first time it had been done in this country.
One of only three men to have completed the stunt, Sinclair is the first to land a double back-flip over ramps spaced 16m apart - 4m further than for the two American riders who had done it previously.
Sinclair (24) said his first reaction on touching down safely was a feeling of "big relief".
It was only the second time he had accomplished it on land, having performed the trick once on ramps in Spain and another into the Sydney Harbour.
Staring down the run-up to the specially designed ramp that propels his 125kg, 250cc dirt bike almost 16m into the air, he visualized the aerial acrobatics he was about to undertake.
Accelerating flat out, he took off and rotated almost twice as fast as when performing a standard back-flip.
"It feels so amazing to finally get that first one away and I am so glad I got to do it on tour with all of my riding buddies.
"It felt so good when they all ran up to congratulate me," Sinclair said, referring to the Crusty crew he has been riding with for the past five years.
Coming from a motocross background he became enamoured with the higher-flying antics of freestyle motocross (FMX) and made the switch.
For someone who lists crashing as one of his pet hates and the no-handed back flip as his favourite trick, it is a surprise that he has only two broken bones to his name: a wrist in 2005 and a collarbone last year.
"I'm the lucky one," he said.
Many of his compatriots have enough metal in their skeletons to send the security scanners into a frenzy at the countless airports the Crusty Demons pass through on their global tours.
Tough guys one and all, they don't wear any specialised safety gear, preferring a simple back protector under their shirts.
"I plan not to crash," Sinclair said.
He said the double back-flip was so dangerous he practised it into foam beds and saved the real deal for show time.
His one plea for the Carisbrook Crusty fans next Saturdaywas for them to make their support vocal to ensure he was well "pumped".
"The crowd gets me going and I go for it."
