Flat spot

In automobile parlance, a flat spot occurs when the driver presses the gas pedal and there is a delay in the engine's response.

[3] Many engines, especially modified ones, still have flat spots in the torque curve due to resonances in the intake system, although manufacturers try to eliminate these by use of a plenum chamber, careful design and testing.

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.

These reduce or avoid the problem by cradling the lower part of the tire tread and preventing the usual deformation where it rests on the ground.