Coilovers: The Technical Guide for Your Chassis

Unlike a fixed "shock absorbers + lowering springs" kit, a threaded coilover (or simply coilover) is a suspension unit with a threaded body. This design lets you screw or unscrew a collar (the lower spring perch) to adjust ride height to the millimeter.

But the benefit isn't only cosmetic. Technically, coilovers let you balance the weight at each wheel ("Corner Balance") for neutral, ultra-precise handling in spirited driving or on track.

The Fundamentals: Main Springs and Helper Springs

On high-performance models, you will often notice two stacked springs:

• The main spring (Main Spring): This is what defines the suspension stiffness (expressed in N/mm or Lbs/inch).
• The helper spring (Helper Spring): A small, soft spring that keeps the main spring under tension when the suspension is fully extended (wheel lifted), preventing any dangerous play.

Comparing the Giants: Which Brand for Which Use?

1. Bilstein: The Benchmark in Monotube Technology

German manufacturer Bilstein is renowned for its UPSIDE-DOWN technology (inverted shock absorber).

Technical note: Their flagship models, such as the B14 (adjustable height) or the B16 (height and damping adjustable simultaneously), use a gas-pressurized monotube design. This provides better heat dissipation and a quicker piston response to small road imperfections.

Bilstein coilovers

2. Eibach: The Master of Progressive Springs

Although originally a spring manufacturer, Eibach offers the Pro-Street-S range.

Technical note: Eibach often relies on stainless steel for its shock bodies (stainless technology) and on progressive-rate springs. The spring is soft over the first few millimeters for comfort, then stiffens under heavy loads to limit body roll.

The Eibach range

3. ST Suspensions: KW Technology for Everyone

A brand of the KW Automotive group, ST Suspensions (notably the ST X and ST XA ranges) uses KW valving and engineering.

Technical note: Unlike KW "Inox-Line" units, ST coilovers use galvanized steel bodies. They are the ideal choice for those who want the kinematics of a motorsport suspension with rebound adjustment (on the ST XA) at a more affordable price.

ST Suspensions parts

4. AP Sport: The Best Balance of Quality, Price and Performance

Also under the KW group umbrella, AP Sport targets tuners looking for real-world effectiveness without unnecessary options.

Technical note: Their coilovers feature fixed factory valving to offer a "Sport-Street" compromise. This is the perfect solution for a significant drop while keeping damping consistent with the reduced suspension travel.

The AP Sport range

Summary Table: Choose Based on Your Needs

The Importance of Installation and Alignment

Installing premium-brand coilovers is only 50% of the job. Once the vehicle is lowered, the alignment angles (camber, toe, caster) change.

Tip: After installation, a full wheel alignment is essential. On heavily lowered vehicles, adding adjustable camber plates may be necessary to optimize the tire's contact patch in corners.

Need Technical Assistance?

Choosing a coilover kit depends on your vehicle and your budget, but above all on your intended use (street, mixed or 100% track).

Our Hubshop experts know the specifics of each brand and can steer you toward the valving best suited to your expectations.