How do I fix this Script.Disabled/Script.Enabled script for my car?

I'm trying to make a script that basically detects a vehicle seat's speed, and if it is greater than or equal to 30, then a script inside a part called "HitBox" is enabled. What am I doing wrong here?

if game.Workspace.BigCar.VehicleSeat.Velocity.Magnitude >= 30 then
	script.Parent.Parent.HitBox.Script.Disabled = false
end

Keep in mind that I tested the other script alone without this part and it works fine, it's just this part.

the code is only being run once, you would have to keep checking for the speed because at the start, the speed is prob gonna be 0, and that's what the code will receive