What Is a Coilover? | Adjustable Suspension Explained

A coilover is an aftermarket suspension unit combining a coil spring and shock absorber into one adjustable assembly, letting you change ride height, stiffness, and handling characteristics.

A coilover—short for “coil over shock absorber”—replaces your car’s factory strut or spring-and-shock setup with a single threaded unit that integrates the spring wrapped around the damper. Unlike standard suspension, aftermarket coilovers let you adjust ride height, spring preload, and damping settings (rebound and compression). That adjustability is what makes them the go-to choice for lowering a car, sharpening cornering, or dialing in a track setup without swapping parts.

This article covers how coilovers work, what you can adjust, how to measure for a custom set, and the real-world tradeoffs you should know before buying.

How Coilovers Work

A coilover assembly has a shock absorber (damper) running through the center of a coil spring, all mounted on a threaded strut body. Turning the lower spring perch changes the ride height—often by several inches—while adjusting the spring preload changes how much the spring compresses under the car’s weight. High-performance kits add 32-way damping adjustment to fine-tune how stiff or soft the ride feels over bumps and through corners.

The key difference from a factory strut: factory “coil-over” units are sealed, non-adjustable assemblies. An aftermarket coilover lets you lower the car 1–4 inches, choose your spring rate, and tune the dampers for street comfort or track grip. Ride Tech, QA1, and Bilstein all produce kits using monotube shock technology, which Bilstein says offers better oil control and responsiveness than older twin-tube designs.

What Can You Adjust?

• Ride height: Lower or raise the car by turning the spring perch on the threaded body. Most kits offer 1–4 inches of adjustment.
• Spring preload: Tightening the spring perch compresses the spring before it takes the car’s weight, changing how it responds on initial bumps.
• Rebound damping: Controls how fast the shock extends after compressing—slower rebound keeps the tire planted through corners; faster rebound improves comfort on rough roads.
• Compression damping: Controls how fast the shock compresses when hitting a bump. Stiffer compression reduces body roll but transmits more impact to the cabin.

Higher-end kits offer independent adjustment for rebound and compression (often 32 clicks each), while budget-friendly coilovers may use a single knob that adjusts both together. If you’re ready to buy, our roundup of budget-friendly coilover kits can help you pick based on price and vehicle fitment.

How to Measure for Custom Coilovers

Factory replacement coilovers bolt right in, but custom-fit units—common for race cars, off-road builds, and solid-axle vehicles—require precise measurements. QA1’s official guidelines lay out the steps for a solid axle setup:

1. Jack the chassis to your target ride height and measure between the upper and lower shock mounts. This is your “ride height” shock length.
2. Jack the axle up until it hits full bump (touching the frame). Measure the mount-to-mount distance, then subtract 1 inch—this accounts for the internal bump stop (5/8 inch) and exposed shaft (3/8 inch), preventing the shock from bottoming out internally.
3. Lower the axle to its natural droop limit (check for binding against steering or driveshafts) and measure again for the extended length.
4. Weigh the vehicle front and rear, including unsprung weight (wheels, tires, brakes). For a solid axle, calculate spring rate as: (vehicle weight – unsprung weight) ÷ (30% of the spring’s free height) ÷ 2.
5. Check clearance—turn the wheels lock-to-lock and flex each side of the axle independently to ensure the spring diameter clears tires and body panels at full articulation.

Also remember that coilovers ride stiffer than OEM springs—you trade some daily comfort for sharper handling and lower stance.

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