Tire dynamics: Self-aligning torque

Many people see tires in two ways, flat or inflated, and that's all. Beyond the visible inspection of a tire, few are aware of the crucial role a tire plays in the grand scheme of automotive design. Remembering, though, that tires are the only part of your vehicle in constant contact with the road, you start to see how obviously important they are. While tires are constructed and manufactured to offer specific performance capabilities to specific vehicles, each and every tire will experience varying levels of the same tire dynamics.

These tire dynamics are determined and controlled by tire manufacturers through extensive tire testing. Manufacturers test their tires under several different conditions in order to see what combinations of characteristics work best for a tire's intended use. Generally, when the driving conditions change, the tires respond differently. However, one tire dynamic that remains relatively consistent regardless of the vehicle or the tires applied to it is that of self-aligning torque.

What is Self-Aligning Torque?

Self-aligning torque is also referred to as aligning torque as well as SAT and Mz. At its essence, self-aligning torque is the torque (a force that produces rotation) developed by the tire when you're cornering (which means turning). It aids in steering the vehicle. This tire dynamic is directly affected by centrifugal force, lateral force, cornering force, the slip angle, and relaxation length. The direct result of these forces is torque, and they ultimately help a vehicle complete a turn. Drivers experience this phenomenon on a daily basis.

Let's consider self-aligning torque in a daily driving scenario. You're sitting at a stop sign. It's your turn to go, so you rotate your steering wheel to make a simple turn. As you come out of the turn, your vehicle straightens itself out. There's no need for you to undo the turn or re-steer the vehicle in order to drive straight ahead. You just experienced self-aligning torque.

Self-Aligning Torque Variables

Some of the variables that can affect self-aligning torque have already been mentioned but there are others. One of those variables, as you can now guess, is the vehicle's tires. As a vehicle enters a turn of any sort, whether in a sharp or wide angle, self-aligning torque will respond to the cornering force and cornering power of the tire.

The cornering force responds to the slip angle of the tire, which will vary greatly depending on the tire's shape, tread pattern, and the materials used in it. A tacky, low-profile, high-performance tire will respond more quickly than that of a tire that's been designed for use on an SUV. Regardless of the tire, self-aligning torque will also be affected by the overall weight of a vehicle, the speed at which a turn is approached, and the actual road surface being driven on.

As you can see, tires play a major role in how you turn and how your vehicle corrects itself coming out of a turn. High-quality tires will help your vehicle do the work for you. On the other hand, low-quality tires can make turning much more difficult. That's only one small part of driving that can be negatively affected by poor quality tires.