Back in the 70s I went to a fundraiser for some desert racer/stunt man who'd fallen on hard times and one of the guest speakers was Bud Ekins. During the Q&A after his entertaining but self congratulatory talk, the subject of the Great Escape came up. One member of the audience, I think it was British USGP promoter Gavin Trippe (if it wasn't him, it was one of his Brit mates) asked "What part did Aussie rider Tim Gibbes have in the filming of the jump"? Old Buds eyes nearly popped out of his head and said that Tim had done much of the preliminary riding leading up to the jump but that he (Ekins) had actually done the jump. Bud wasn't impressed at all by the question and you could see that he was shaken by this attempt at denting his legend. He quickly changed the subject back to how brilliant he was and it wasn't long before he ended his part of the show and exited, stage right. Later over a beer I was amongst a group of Checkers club members who were taking about 'the jump' and one bloke, coincidentally another pom, stated that he'd been told by McQueen himself that Gibbes had actually done the jump but as he wasn't a member of the Stuntsmens Union the credit went to Bud Ekins who was the official lead stuntsman on the film and McQueens best mate.
This explanation seems pretty logical considering the strength of the stunt community and their union. A few years ago I read in a British magazine, possibly Classic Bike that Tim Gibbes had done the jump and I remember Roy East saying to me that the rider in the photo of the jump looks very much like Gibbes who had a passing resemblence to McQueen, including blonde hair. Ekins looked nothing like McQueen and would have had to have undergone some solid disquise work. Roy reckoned that the Gibbes theory was spot on. As Gibbes and Easty were mates, I reckon Roy knew the real story. He didn't exactly say that Tim had done the jump but you could tell that he knew.
Below is Bud Ekins "official" explanation of the jump
Well that was shot on a Monday and on Sunday, Steve, myself, an Australian motor-cross racer and Tim Gibbs, an excellent rider, we all went out to where they were going to do that scene and the effects man put a piece of string across at all these different heights. The first time I'd take a run at it and jump maybe two feet off the ground and then we would take a shovel and dig this natural ramp, changing the angles on it. And I'd jump 4, 6, 8 feet and then when we reached 10 feet we said that's it--we had the ramp and the speed. Nobody knew we were up there so when it comes to Monday nobody said we'd already done it. Finally when I went ahead and did it we did it in one take. It seemed I was up in air forever--10 or 12 feet high and 120 feet distance jumped. When I was in the air it was dead silent."