What is the primary effect of under-inflated tires on a vehicle's performance?

The primary effect of under-inflated tires on a vehicle's performance is indeed poor handling. When tires are not properly inflated, they cannot maintain their intended shape and contact patch with the road. This can lead to decreased grip, reduced responsiveness to steering inputs, and overall compromised vehicle stability. Furthermore, under-inflated tires tend to flex more than properly inflated ones, leading to increased rolling resistance, which affects acceleration and can make the vehicle feel sluggish. Appropriate tire pressure is crucial for ensuring the best handling characteristics and safety of the vehicle, as it directly impacts the interaction between the tires and the road surface during various driving conditions.