What happens to turning radius as speed increases?

• A. Increases
• B. Decreases
• C. Remains The Same
• D. Varies With Direction

Answer: (A)

As speed rises, keeping the same sharpness of a turn requires more lateral force from the tires. The needed lateral force to follow a curved path is F_y = m v^2 / R, where v is speed and R is the turning radius. The tires and road can only supply a finite amount of lateral grip (roughly proportional to normal force and tire condition). So when you increase speed with a fixed steering input, the demanded lateral force grows with v^2, and the available grip may not be enough to sustain the same curvature. The result is a larger turning radius—the car follows a wider arc.

In practical terms, this is why higher-speed turning tends to feel less sharp: the tires can’t provide the same lateral pull needed for a tight turn at that speed. If you needed to maintain the same sharp turn, you’d have to exert more steering or slow down.