Caster is the angle of your vehicle's steering pivot when viewed from the side. It's a cornerstone of wheel alignment that primarily affects steering stability and the wheel's ability to return to center after a turn. Think of the front forks on a bicycle—they are angled forward, which is positive caster. This angle creates a self-centering effect for the steering, making your car drive straight with less effort from you.
The caster angle is measured in degrees. Positive caster means the steering pivot axis is tilted toward the rear of the vehicle. This is the standard for almost all modern cars. It provides high-speed stability and that important return-to-center feeling. Negative caster, where the axis tilts toward the front, is rare and generally results in unstable, nervous steering.
| Vehicle Type | Typical Caster Angle Range | Primary Effect |
|---|
| Standard Passenger Car | 3 to 7 degrees | Optimizes stability and steering feel. |
| Performance/Sports Car | 7 to 10 degrees | Increases high-speed cornering stability. |
| Off-Road/Lifted Truck | 0 to 4 degrees (or more) | Preuces steering effort at low speeds. |
| Classic Car (1970s or older) | Often 0 to 2 degrees | Softer steering feel, less responsive return. |
While caster doesn't directly cause abnormal tire wear like incorrect toe or camber can, an uneven caster angle from side to side can cause the vehicle to pull toward the side with less positive caster. If your car drifts to one side on a straight, level road, a caster imbalance is a likely culprit. Correcting caster is crucial for predictable handling and safety, especially when combined with precise camber and toe adjustments.
