Revealing mistake: When Bud and Wes take competitive turns riding the bull at the presumed high speeds, the bucking patterns and timing aren't consistent. A few times either man goes less than 15 seconds on a mid speed rather than full on bucking. Which even for a practice doesn't add up, and wouldn't fly during a competition.
Urban Cowboy (1980)
1 revealing mistake - chronological order
Directed by: James Bridges
Starring: John Travolta, Scott Glenn, Debra Winger, Madolyn Smith Osborne
Other mistake: When Bud is hit by the mechanical bull, he jumps up shouting "You broke my godd**n arm.", and this is a point thought the next 45 minutes or so. The cast he is seen wearing however is only given for a broken thumb, not a broken arm, which is where he was hit.
Trivia: Gilley's Night Club actually existed in Pasadena, Texas (was owned by Sherwood Cryer) Some scenes were also filmed at 2200 South Main St, and 2016 South Main St., in Houston, Texas.