A flat spot is an area of your tire that has become flat due to the weight of the vehicle pressing down on the tire for an extended period of time. This typically occurs when the parking surface is cold. Flat spots can easily happen with trailer tires because trailers tend to sit for extended periods of time. In most cases, these flat spots will round out again after the tire has heated up from traveling. However, a flat spot can be permanent. A permanent flat spot could be a sign of damaging moisture buildup, especially if the trailer is parked in the grass.