Caster

Caster is the angle of a car's steering axis when viewed from the side, measured against a vertical line perpendicular to the ground.

To understand caster angle, imagine drawing a line through the steering pivot points on your front wheel—from the top mounting point down to the bottom. This line is called the steering axis. Caster measures how much this line tilts forward or backward compared to a straight vertical line. Think of it like the angle of a motorcycle's front fork, which always leans back slightly.

Most modern vehicles use positive caster, meaning the steering axis tilts toward the rear of the car at the top. Picture a shopping cart wheel—it trails behind the pivot point, which is exactly what positive caster does for your car's front wheels. Negative caster tilts the opposite way, toward the front of the vehicle, but this is rarely used in modern cars because it creates unstable steering.

The main benefit of caster angle is self-centering steering. When you turn the wheel and then let go, positive caster helps the wheels naturally return to pointing straight ahead. This happens because the steering axis intersects the ground slightly ahead of where the tire contacts the road, creating what engineers call "trail." The larger this trail distance, the stronger the self-centering effect.

Regular passenger cars typically run between 3 and 5 degrees of positive caster. This provides good stability for everyday driving without making the steering wheel too heavy to turn. Race cars, however, use much more aggressive caster angles—often exceeding 7 degrees, with some Formula 1 cars running over 10 degrees. These extreme angles improve high-speed stability and help the tires lean into corners more effectively.

Increasing caster angle does make steering heavier, which is why race cars with high caster angles rely on power steering. For drivers, more caster means better road feedback and a more connected feeling to the front wheels. This helps professional drivers feel exactly what the tires are doing during aggressive cornering.

Race engineers adjust caster settings to suit different tracks and conditions. A high-speed oval might benefit from more caster for stability, while a tight street circuit might use less to reduce steering effort. Some teams even use different caster angles on the left and right sides—called caster split or cross caster—to fine-tune how the car handles in specific corner directions.

Caster angle is one of three primary suspension alignment settings, along with camber and toe. Together, these adjustments allow teams to optimize how tires contact the road surface, maximizing grip and vehicle control during competition.