Jessi Combs -- the "Fastest Woman on Four Wheels" -- crashed her jet-car because her front wheel gave out.
According to the Harney County Sheriff's Office ... the front wheel of Jessi's jet-powered car suffered a mechanical failure before her fatal crash, and the front wheel assembly most likely collapsed as a result of hitting an object during her attempt at breaking her own land-speed record.
The Sheriff released the findings Monday after completing an investigation into the crash ... and they say the front wheel failed when Jessi's jet-car reached around 550 miles per hour.
Jessi's cause of death was also determined to be blunt force trauma to the head, which the Sheriff says occurred before her race vehicle was engulfed in flames following the crash.
As we reported ... Jessi's jet-powered car crashed and killed her in August in the Alvord Desert in Oregon. Photos of the wreckage showed her 56-foot-long jet-car -- the North American Eagle -- completely destroyed, and the footage we obtained shows her traveling at incredible speeds before the crash.