Maximum speed for a car over a hilltop without losing contact

[DBaima22]

A person drives a car over the top of a hill, the cross section of which can be approximated by a circle of radius r=250m. What is the greatest speed at which he can drive without the car leaving the road at the top of the hill?

I know that the maximum speed occurs when the normal force= zero. And by my calculations v_max=√rg (where r is the radius and g is the acceleration of gravity)

Is this all I need? Am I missing anything?

 

[Dick]

Seems ok to me. What to you think you might be missing?

 

[DBaima22]

I didn't think there was anything missing, this is just me being paranoid I guess. Thank you