How to Adjust Coilovers: Height, Preload, and Damping

A coilover bundles a spring, shock, and strut housing into one unit, and that is what makes it adjustable in ways a stock spring-and-shock setup is not. See what a coilover actually is for how the parts fit together before you start turning anything.

Ride height is set by threading the lower mount, or on some kits the shock body itself, up or down a set of threads, independent of how the spring is loaded. Preload is how snug the spring sits between its two perches at full extension, controlled by a separate locking collar just below the spring. Damping is how fast the shock compresses and rebounds, controlled by a knob or dial, and on single-adjustable kits one knob moves compression and rebound together while double-adjustable kits split them into two separate dials.

Height and preload adjustments are done with the car's weight off the suspension, so you need a floor jack and a pair of jack stands rated for the corner weight, plus wheel chocks. A coilover spanner wrench turns the knurled locking collars without chewing up the finish the way pliers or a hammer and punch do; most kits include one, but a spare pays for itself the first time you drop one under the car.

You'll also want a tape measure for setting preload and checking ride height, a torque wrench for the strut mounting hardware once you're done, and a notebook or phone camera to record the click count and collar position on each corner before you touch it, in case you want to return to the stock setting.

With the corner off the ground and the spring unloaded, loosen the upper locking collar with the spanner wrench, then thread the lower mount or spring perch assembly up to raise the car or down to lower it. Snug the locking collar back against the perch once you're at the height you want, then lower the car onto the ground and measure ride height at a fixed reference point, such as the center of the wheel arch to the ground, on all four corners.

Adjust one corner at a time and recheck the measurement before moving to the next, since threads can bind slightly and give a different result than the number of turns alone would suggest. Front and rear ride height on most coilover kits adjust independently, so matching a target rake (a slightly lower front than rear, or level) takes a few rounds of small adjustments and rechecks rather than one pass.

Preload is not the same adjustment as ride height, even though winding the wrong collar can change both. Loosen the lower lock ring so the spring can move freely, then turn the upper spring seat down until it just contacts the spring with no gap and no compression, which is zero preload. From there, thread the seat down further by the amount your kit calls for, and lock the ring against it.

Fortune Auto's coilovers ship with no preload set at the factory, specifically so the springs aren't under load during shipping, and the company's own adjustment guide calls for about 1/4 inch (0.25 in) of preload on MacPherson strut front ends and about 1/8 inch (0.125 in) on double wishbone suspension, measured from the top of the spring to the bottom with a tape measure and a 5mm Allen key plus spanner wrenches to turn the collars. Not every brand works the same way: BC Racing's coilovers, by contrast, come with preload already set at the factory, so there's nothing to add out of the box unless you're replacing a spring with a different rate. Check which camp your kit falls into before assuming it needs preload dialed in from zero.

Too much preload stiffens the effective spring rate and can make the ride bouncy; too little lets the spring rattle loose in the perch over bumps and at full droop. Neither extreme is a big performance issue on its own, but both are easy to avoid by setting a modest, even amount on both sides of an axle.

Damping adjustment changes how fast the shock's oil moves through its valving, which changes how quickly the suspension compresses over a bump and rebounds afterward. On a single-adjustable coilover, one knob, usually on top of the strut, moves compression and rebound together. On a double-adjustable kit, compression and rebound each get a separate dial, often one at the top of the shock and one lower on the body, so they can be tuned independently for a stiffer corner-entry feel without making the ride harsh everywhere else.

BC Racing ships its coilovers already set to a moderate drop with the damping just above mid-range, which the company describes as a good all-around street setting that's fully adjustable from there. Turning the knob toward full hard firms up the ride and resists body roll at the cost of comfort; turning toward full soft does the opposite. Work in small steps, a few clicks at a time, and drive the car between changes, since the difference between settings can be hard to judge by feel alone until you've tried a few.

Brands differ enough in click count, numbering direction, and starting point that a setting recommended for a Tein kit or a KW kit won't translate directly to a BC Racing or QA1 coilover. Start from your kit's own manual, then adjust from there based on how the car feels.

Once height and preload are set the way you want, re-torque the strut-to-knuckle and top mount hardware to the spec in your kit's manual, since loosening a locking collar can let other fasteners creep if they weren't fully seated to begin with. Bounce each corner a few times and recheck the ride height measurement, because settling after the first few miles is normal.

Any change in ride height moves camber and toe out of factory spec, so book a four-wheel alignment after adjusting, not just after the initial install. If you changed height by more than an inch or so, expect to need camber bolts or aftermarket camber arms to get back into the adjustable range; see the coilover installation and cost guide for what that typically adds to a shop visit.

The most common mistake is adjusting only one side of an axle and assuming the other matches, which leaves the car pulling or sitting crooked. Measure both corners every time, even for a small change. A second common mistake is confusing the preload collar with the height collar on kits where they sit close together, which changes the drop without the spring tension you intended, or the other way around.

Skipping the alignment afterward is the mistake that costs the most down the road: uneven tire wear from a camber or toe change can outlast the money saved by not booking a shop visit. And running damping at full hard or full soft for an extended period, rather than as a brief test, stresses the valving in a way most manufacturers warn against in their own manuals.