In chassis layout, the A-line serves as a primary reference point. This line connects the spin centers of the front wheels. Aligners use this line to measure wheelbase consistency and steering axis geometry. If a car hits a curb and bends a control arm, the wheel will shift backward. This changes the angle of the front wheels relative to the A-line, causing pulling and tire wear.
Mechanic Glossary
A-Line
A geometric reference line drawn between the centers of the front wheels, used in suspension alignment and chassis blueprinting.
Frequently Asked Questions
The geometric reference axis connecting the centers of the front wheels, used to check chassis squareness.
It pushes one wheel back, throwing off the wheelbase measurement and skewing the alignment angles.
It is difficult without a professional alignment rack. You can approximate it by measuring distance from the front wheel center to a fixed point on the rear axle.