Could I disable the spring of the vehicle?

Could I disable the spring of the vehicle?I mean the tires of vehicle will not go up and down even in the bumpiness.

I have tried this way,like the following.

function WheeledVehicleData::onAdd(%this,%obj)
{

for (%i = %obj.getWheelCount() - 1; %i >= 0; %i--) {
%obj.setWheelTire(%i,DefaultCarTire);
// %obj.setWheelSpring(%i,DefaultCarSpring);
%obj.setWheelPowered(%i,false);
}

}

just disable the line of setting spring.But It does not work,how can I do?