Josh Pillinger, 24, lost control of the powerful motor after girlfriend Emily Dean, 24, hired it as part of a £99 "race day experience".
She had brought him the racedriving experience as an early 25th birthday present when the tragedy happened.
Emily – who was sat in the passenger seat – suffered minor injuries and was taken to hospital.
Police are now investigating Josh's death at the Mid Wales Activity Centre, in Pontrhydfendigaid, near Cardigan, used for rallies, quad bikes and extreme sports.
In a tribute, Emily said: "I lost my soul mate, best friend and the love of my life.
"I'm completely heartbroken and lost for words. I miss him so much and I'm desperate for him to walk through the front door one day or speak to him again.
"I have the best memories with him.
"Josh was truly the best person I have ever met, I spent nine solid years with him everyday and I love him so much.
"I will forever be lost without him, I will never forget him he will always be apart of my life! R.I.P Josh I will love you always."
His family added: "If you ever had the pleasure of meeting Josh, I'm sure you will never forget him.
"He was one of those people who had such a positive impact on the lives of everyone fortunate enough to meet him.
"We miss him and the way he used to make us all laugh so much, every single day."
Dyfed Powys Police said they were investigating the crash – and an inquest is expected to be announced soon.
A spokesman said: "Dyfed-Powys Police was called to a single-car collision at a private race track at Mid Wales Activity Centre, Pontrhydfendigaid.
"Sadly the driver, a 24-year-old man from Bristol, died at the scene. Our thoughts are with his family.
"Police are investigating the circumstances surrounding the collision.
"No further information is available at this time."
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