A tire is considered flat when the tire pressure is what percentage below the manufacturer's recommendation?

A tire is considered flat when the tire pressure is significantly below the manufacturer's recommendation, specifically when it is 20% below the recommended level. This threshold is important because when tire pressure drops this low, it can negatively affect the vehicle's handling, fuel efficiency, and safety. Maintaining proper tire pressure is crucial for both optimal performance and minimizing the risk of tire blowouts, which can lead to hazardous driving conditions.

The other percentages listed do not signify the point at which a tire would typically be deemed flat by most safety standards. A smaller percentage, such as 5% or 10%, may not significantly impair the tire's functionality, while 30% would indicate a much more severe deficiency in tire pressure, already exceeding common safety thresholds. The 20% level strikes an essential balance, marking a critical point for safety and performance considerations.