A caster sweep is a controlled steering movement used by the aligner to calculate caster and Steering Axis Inclination. The quality of the result depends on the actual steering angle, stable target tracking and unrestricted wheel movement.
Caster and SAI are calculated from wheel-angle changes.
The requested sweep angle must be reached accurately.
Turn plates must be centered and free.
Repeatability is the best check of sweep quality.
Measurement principle
As a steered wheel turns, its camber changes according to the orientation of the steering axis. The aligner measures this change along with the actual steering angle and calculates caster and SAI. A larger controlled sweep can improve the geometric signal, but the correct sweep is the one supported by the vehicle, bay and software procedure.
Because the calculation uses movement, any restriction or target interruption can alter the result even when the straight-ahead camber reading appears stable.
Preparing for the sweep
- Center the turn plates before positioning the vehicle.
- Remove plate pins only after the vehicle is secure.
- Confirm front tires are centered on the plates.
- Keep rear slip plates free so suspension movement is not restricted.
- Make sure the steering wheel and front wheels begin near straight ahead.
- Verify target visibility through the full steering range.
Sweep-angle options
| Sweep range | Typical use | Consideration |
|---|---|---|
| Small-angle sweep | Limited-clearance or quick workflow | Requires accurate steering-angle tracking. |
| Standard sweep | General passenger-vehicle measurement | Balance of speed and geometric signal. |
| Large-angle sweep | Diagnostic or supported high-angle procedure | Check tire, body and plate clearance. |
| Live or repeated sweep | Adjustment verification where supported | Maintain consistent vehicle conditions. |
Common sweep errors
Stopping short of the requested angle, steering past the target and returning, pressing the brake, allowing a tire to contact a stop or moving the vehicle on the rack can all affect the calculation. Follow the on-screen direction and use smooth steering input. Do not use excessive force against a binding steering system.
Using sweep results
Caster supports stability and pull diagnosis. SAI and included angle support component and structural diagnosis. Evaluate the values together with ride height, setback, camber and physical inspection. A single sweep result should not be used to condemn a knuckle, strut or control arm without confirmation.
Best-practice procedure
- Complete compensation and settle the vehicle.
- Start with the steering near center.
- Follow the requested turn direction.
- Reach the indicated angle smoothly and hold as prompted.
- Turn through center to the opposite angle.
- Return to center without disturbing the target assemblies.
- Review repeatability and repeat if necessary.
Frequently asked questions
Why do some systems use different caster sweep angles?
Different camera systems and procedures can calculate the geometry from different controlled ranges. Use the angle requested by the aligner and supported by the vehicle.
Can the brake be pressed during the sweep?
Normally the wheels should turn freely on the plates. Follow the vehicle and aligner procedure if brake application is specifically requested.
Why does caster change after adjustment even before another sweep?
A live estimate may update, but the final calculated value should be confirmed with a fresh sweep after major changes and tightening.
Technical content reviewed for TreadPlus Learn v1.0 · Updated July 16, 2026