Jeremy Durst, 30, from Miami, Florida, signed up for the Motorama racing event, in Harrisburg, Pennsylvania, and enlisted officials in his proposal to Sara Frank, 30.
Footage shows Jeremy apparently losing control of his bike on a bend and it sliding away into a barrier.
The keen biker went down as if he was injured, rising to his feet and then turning around so that his back was to the crowd.
An official ran towards him, sneaking him the ring in the process, before worried Sara rushed from the stands towards her boyfriend.
When she bent down to check on her partner, he was on one knee holding up the ring.
The rider was also handed a microphone to pop the question, which Sara nodded to in delight and then said 'Yes'.
Asked if she had any idea of the proposal, she said: 'No I had no idea, I thought he just crashed.'
He came up with the unique way of proposing because it would make sure his girlfriend's family and friends would be in attendance, he said.
Jeremy bought a new Kawaski KX450 bike and entered the race, which he thought would mean that his girlfriend, and their family, would not suspect a thing.
With thousands set to be in attendance, he contacted the race organizers to pitch his idea, saying he would pass one of them the ring before the race.
During the race he would ride around in last place, and then fake a wreck on his last lap.
Donning a GoPro, Jeremy did just that – but during the race, he unsuspectingly happened to pass another racer, meaning he would need to slow down to let that rider past.
This meant Jeremy actually overshot the safe crash zone he had identified, and so he had to opt for a fake crash on a separate turn instead.
The elaborate proposal place on February 16, and the couple are expecting a baby in November. They plan to get married next year.
Jeremy said: 'I didn't get slapped as hard as I expected for scaring her, so it was all good.
'Honestly, it was an indescribable feeling – like I hit the lottery.'
Sara said: 'I had a range of emotions throughout each stage of the surprise.
'At first, I was confused. I was not sure what was wrong with the bike to cause him the crash that way.
'Then I was told to go check on him and then my confusion turned to worry as I saw him kneeling on the ground. I was hoping he wasn't hurt.
After he pulled out the ring, I think it is obvious from the video that I was in complete and total shock – I did not see this coming at all.
Once the shock of what was happening wore off and I realized he was not hurt I was overjoyed.
'Honestly, it was an indescribable feeling – like I hit the lottery.'
Sara said: 'I had a range of emotions throughout each stage of the surprise.
'At first, I was confused. I was not sure what was wrong with the bike to cause him the crash that way.
'Then I was told to go check on him and then my confusion turned to worry as I saw him kneeling on the ground. I was hoping he wasn't hurt.
'After he pulled out the ring, I think it is obvious from the video that I was in complete and total shock – I did not see this coming at all.
'Once the shock of what was happening wore off and I realized he was not hurt I was overjoyed.
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