If the turning radius (toe out on turns, or TOOT) is out of specification, what part or component is defective?

When the turning radius, also known as toe out on turns (TOOT), is out of specification, the most likely component that is defective is the steering arm. The steering arm plays a crucial role in the steering geometry by connecting the steering linkage to the wheels. If the steering arm is bent or damaged, it can alter the angles at which the wheels turn in relation to each other, leading to excessive toe out during turns. This misalignment affects the vehicle's handling, steering response, and tire wear, which is why ensuring that the steering arm is in good condition is essential for proper steering performance.

The other components mentioned may affect different aspects of the steering and suspension system, but they do not directly influence the turning radius in the same way the steering arm does. For instance, a bent spindle or control arm could influence ride height or tire alignment, but they would not specifically cause a deviation in toe out on turns.