An investigative team is tasked with determining the root cause of a specific model of car tyre that is failing at an unusually high rate. The team's first step is to subject a large sample of new, unused tyres of that model to a series of high-speed, high-stress endurance tests in a controlled laboratory setting. The results show that the tyres perform as expected and do not exhibit the failure mode under these conditions, leading the team to conclude that the fundamental design of the tyre is sound.

Based on this conclusion, analyze the situation and identify two distinct categories of potential causes that the investigators should now explore. For each category, provide a brief justification explaining why it is a logical area for further inquiry.