Which of these would cause the tires to wear in the center of a tire tread?

When tires wear in the center of the tread, it typically indicates a condition related to tire inflation. Over-inflated tires have an increased pressure that causes them to bulge outward at the center of the tread. As a result, the surface area of the tire contacting the road is reduced to the center section, leading to accelerated wear in that central area.

In contrast, under-inflated tires tend to wear more on the outer edges due to the increased flexing of the sidewalls, distributing the weight unevenly. Worn suspension parts could contribute to uneven tire wear by affecting the vehicle’s handling and weight distribution but are not specifically associated with center tread wear. Improper alignment usually leads to uneven wear patterns across the tire's tread, but again, not specifically limited to just the center.

Thus, over-inflation is the primary cause of center tread wear, making it the correct response in this context.