Is it time to replace your race suit? Let’s get you track-ready. Ride Height, Preload And Getting A Coilover Setup Right
A coilover kit has two separate adjustments on it and they get mixed up more than anything else we fit. One is the threaded lower bracket that the whole strut sits in, and that’s ride height. The other is the preload collar on the spring perch, and that sets how much the spring is already wound up before the car’s weight even reaches it. They sit within reach of each other on the strut, which is exactly why people wind the wrong one.
Get the two mixed up and the car can end up sitting at the height you wanted with the setup working against you the whole time.
Ride height is the threaded bracket, not the spring
On a BC Racing coilover the lower mounting bracket screws up and down the body of the damper. Wind it down and the whole strut drops in the mount, which lowers the hub and the car with it. Wind it up and the car rises. The spring travels with the strut either way, so its own compressed length at rest doesn’t change. This is the adjustment to use for ride height, full stop.
Preload is a different job entirely
The preload collar sits under the spring and winds it up before the car’s weight ever touches it. All it does is take the slack out of the spring so it’s seated properly against the perch, or add a bit more tension on top of that. It does not change the spring rate. A 6kg spring is still a 6kg spring whether the collar is backed off or wound hard in, it just changes how much of that spring’s travel has already been used up before the car settles onto it.
Why winding preload for height catches people out
Preload is the ring people reach for because it’s the one closest to hand and it does move the car, just not for the reason they think. Wind more preload in and the spring sits further compressed before the suspension has done anything, so the strut needs to move further before the spring even starts working, and the car does sit a little higher on that spring’s working point.
The problem is what that does to the rest of the travel. Push preload in hard enough to gain real height and you’ve moved the spring’s working range further up, which leaves less room before the strut runs out of downward travel and the spring goes coil bound. On the road that shows up as a harsher ride over bumps and a bang through the strut on compression events that a correctly set up kit would have absorbed. Set height with the bracket and use preload only to seat the spring properly, and neither of those problems turns up.
What to check once it's set
A tape measure at the arch tells you the car is level. It doesn’t tell you the car is balanced. If you’re setting a car up properly, get it corner weighed with a driver in the seat, because a coilover platform lets you correct side to side and front to rear balance in a way a fixed spring setup can’t, and that balance matters more than the number at the arch.
With the car sitting at its finished ride height, check each corner has room to move both ways. A strut sitting near the top of its travel at rest has nowhere left to go on a compression, a strut sitting near the bottom will top out on the first dip in the road. Either way you’ve built a car that looks right stationary and doesn’t work moving. Once height is where you want it, go back over camber and any adjustable arms or drop links, because changing ride height changes the geometry those parts were set against.
Where to go next
For what each BC Racing series is built for and which one suits the way the car’s actually used, the series guide covers that. If you’re fitting to a BMW, the BMW coilover guide lists the range for that platform along with what to check on the listing before you order.
Final thoughts
Ride height and preload aren’t the same adjustment and treating them as interchangeable is how a good kit ends up feeling worse than it should. Set height on the bracket, use preload to seat the spring, then check it with the car loaded rather than empty.
Cameron, GSM Performance
