What is the primary cause of flat spots on a roller carrier?

Flat spots on a roller carrier primarily occur due to the inability of the roller to turn. When the roller is stationary for extended periods or if the roller's turning mechanism is malfunctioning, the weight distribution on a single point can cause a flat area to develop on the wheel. This situation is exacerbated when the roller is left in one position for prolonged durations, resulting in uneven wear and the formation of flat spots.

The other options, while they may relate to roller performance in general, do not specifically address the mechanical dynamics that lead to flat spotting. Excessive weight can cause overall wear but does not directly result in flat spots unless combined with the inability to turn. Poor maintenance, while crucial for the longevity and functionality of the roller, does not singularly lead to this specific issue unless it results in a turning mechanism failure. Similarly, improper use may contribute to wear and tear but is not a direct cause of flat spots compared to the stopping or turning inefficiencies that allow weight to remain fixed on specific areas of the roller.