Air bubbles in your tires are, for the most part, are caused by impacts on the road. Hitting the edges of potholes, minor impacts, hitting a check, and hindrances would all be able to make the sidewall swell in your tires.
Lowering your truck is a choice dependent on the owner attempting to accomplish a specific look instead of improving functionality. Many people think trucks are intended for work purposes and that lowering the suspension and making it less functional is not brilliant.