 A literal flat spot can occur on car tires if the vehicle is parked without moving for some time (generally longer than a week), and the tire deformation at the bottom of the wheel becomes semi-permanent.The flat spot gradually relieves itself when the car is driven but can temporarily give similar symptoms to an unbalanced wheel.Cars being laid up for extended periods, or intermittently-used caravans and trailers, should be kept on axle stands (tyres not in contact with the ground) or have the tires over-inflated to eliminate or reduce this problem.