Johansson and Reynolds clash over his motorbike hobby
The actor is hooked on the high octane pursuit and is planning a summer road trip across Alaska on his new Paul Smart Ducati bike.
But Johansson - who married the Canadian star last year (08) - is terrified a bad accident is waiting to happen.
He recently dodged injury when a car performed an illegal turn and ended up in his path. He had to swerve quickly to avoid it - shaking him up and scaring Johansson.
A source tells the National Enquirer, "She's petrified a serious accident is just around the corner. When she asked Ryan to give up motorcycling, he flat out refused. And that led to a pretty heavy argument."