C/O Spring - 4.125 ID x 11 300# Silver

The QA1 Coil-Over Spring 4.125 ID x 11 300# Silver is a precision-engineered coil spring designed for suspension systems demanding responsive handling and consistent load support. With a 300 lb/in spring rate and 11-inch length, this QA1 coil-over component delivers the tuned compliance needed in high-performance vehicle setups where suspension geometry and ride quality require careful calibration.

Manufactured from steel with a silver powder-coat finish, this spring resists corrosion while maintaining consistent stiffness across extended temperature ranges. The 4.125-inch inner diameter accommodates standard coil-over shock body designs, while the 300 lb/in rate positions this spring in the middle compliance range—stiff enough to minimize body roll and suspension dive under cornering and braking, yet compliant enough to manage bumps and uneven pavement without excessive harshness. Each spring is individually produced to QA1's tolerances, ensuring repeatability when paired with matching components on the opposite side of the vehicle.

This coil spring serves serious builders and tuners working on street performance cars, road-course vehicles, and suspension-focused platforms where spring rate selection directly impacts driver feedback and chassis balance. Off-road applications, autocross setups, and track day builds frequently employ springs in this stiffness range to achieve responsive handling while maintaining adequate ride comfort. QA1 springs are commonly specified by suspension shops and OEM performance divisions when factory springs don't meet the handling targets of a modified platform.

Spring rate selection is fundamental to suspension tuning. A 300 lb/in spring requires approximately 300 pounds of force to compress one inch—higher rates increase stiffness, lower rates increase compliance. Matching spring rates front-to-rear, selecting appropriate ride heights, and pairing springs with compatible dampers (shocks) ensures the suspension system performs as designed. Many builders work with spring rate charts and manufacturer guidance to select the correct stiffness for their vehicle weight, desired handling character, and driving conditions.