Helper, Tender and Main Springs Explained
Helper springs keep your main coilover spring seated on its perch when the wheel hangs, and they add almost no rate at ride height. A tender spring is a softer second spring that gives you a dual rate. The main spring carries the car.
You jack up the rear of your lowered car and the main spring rattles loose on the perch. Or you open a new kit and find a short, flat spring stacked on top of the main one. Is something wrong? Usually not. Here is what each spring does, why some coilover kits ship with an extra one, and when you should add one yourself.
The Main Spring: What Holds the Car Up
The main spring is the big one. It carries the weight of the car at ride height and sets how stiff the suspension feels. When you read a spring rate on a spec sheet, such as 8 kg/mm, that is almost always the main spring.
On a coilover, the main spring sits between the top mount and the spring perch. On full-length kits, you set ride height at the lower mount, and the spring perch sets preload. Preload is measured with the wheel hanging. It is the spring's free length minus its installed length.
Preload does not change the spring rate. At ride height, the car's weight compresses the main spring far past its preload anyway. Our guide to coilover preload covers how to set it.
What Helper Springs Do
Picture the car on a lift. The wheel drops, the damper extends, and the main spring has more room than its length. If it has little or no preload, it goes loose. It can rattle, shift off center or even unseat from the perch. When the wheel comes back down, the spring may not land where it should.
A helper spring fills that gap. It is a short, light spring stacked with the main spring. At full droop, it pushes the main spring onto its seat. With the car at ride height, the helper is usually squeezed flat, so it adds next to nothing to the ride.
Swift makes helper springs for coilovers. Dealers selling them describe their job the same way. They keep the main spring from dismounting the perch during droop travel, with minimal effect on the main spring's rate. They are sold individually, and dealers note you need a pair for an axle.
What Tender Springs Do
A tender spring is a softer spring stacked with the main spring, like a helper. The difference is intent. A helper exists only to keep the main spring seated. A tender is chosen to change how the suspension feels in its first bit of travel.
Two springs stacked end to end work in series. Their combined rate is lower than either spring alone. The math is one over the sum of one over each rate. An 8 kg/mm main with a 2 kg/mm tender gives about 1.6 kg/mm at first. Once the tender coils go solid against each other, only the main spring works, and you are back to 8 kg/mm.
That gives a dual-rate feel: soft over small ripples, then firm as load builds. On a lowered street car, a tender can make sense where you need extra droop travel. Be warned, though. Shops and brands do not all use these words the same way. Some call any stacked spring a helper. Ask what rate the extra spring has and when it goes solid.
Why Some Coilover Kits Ship With Helpers
Ride height and preload pull against each other on some cars. To get the car low, the main spring needs to be short or set with little preload. To keep the damper's full stroke, the damper extends a long way at droop. Put those together and the main spring goes loose before the damper is fully extended.
Engineers solve that with a helper spring rather than a longer main spring. The helper keeps everything seated without changing how the car rides.
Brands make this call per fitment. A BC Racing, KW, Fortune Auto or TEIN coilover kit may or may not include helpers for your car. Check your kit's parts list. If you see a short flat spring on top of the main spring, that is probably it. Leave it in place unless the manual says otherwise.
Helpers are not a fix for running out of travel. If the car crashes over bumps, look at ride height and bump stops first. Our guide on how to set ride height on coilovers is a good place to start.
When to Add a Helper Yourself
Your main spring goes loose at full droop. Lift the car and check. If the spring wiggles freely with the wheel hanging, a helper is the usual fix.
You switched to a shorter main spring. A custom rate or a shorter spring can leave a gap at droop.
You hear clunks when the car lifts or lands. A loose spring knocking on its perch is a common cause.
You cannot add preload without raising the car. On a perch-only kit, the perch sets ride height and preload together, so a helper may be the only clean answer.
Do not add a helper to a spring that already has preload and stays seated. It adds nothing useful there. It just adds parts.
Think of the helper as one small piece of a performance suspension setup. Spring rate, damping, ride height and alignment do the real work. The helper just keeps the main spring where it belongs so those settings stay true.
Fitting Helpers: Adapters, Sheets and Sizes
A helper needs a way to sit on the main spring. Swift's stacked spring adapter kit handles that. Dealers describe it as the piece that lets you stack a flat-wire helper or assist spring on a round-wire main spring. One dealer notes its Swift helpers ship with a stack adapter.
Inner diameter must match. Helpers come in set inner diameters to suit common coilover springs. Measure your main spring's inner diameter, or call us with your kit details, before you order.
Swift also sells thrust sheets. Dealers describe them as letting the spring rotate on its seat as it compresses. A coil spring tries to unwind under load, and the sheet lets it turn instead of binding.
A helper adds a little mass. Part of the spring's mass counts toward unsprung weight, but the wheel, tire, hub and brakes make up most of it. A helper does not change that picture in any way you will feel.
Swift Springs on BC Racing Kits
Swift Springs SPEC-R springs are the upgrade spring option on most BC Racing fitments. They ship standard on HM and ZR kits on most fitments. On other series you add them through a custom build, and we also list a half kit of two Swift springs for BC coilovers. Our guide to BC Racing and Swift Springs covers that pairing. Swift says it was founded in Tokyo in 1997 as the motorsport spring brand of Tokyo Hatsujo.
If you change main springs, check whether you still need helpers. Our guide to spring physics explains why spring length, rate and travel all have to work together. Confirm fitment on the product page, or call 1-800-460-9106 with your VIN and we will check your kit.
Frequently Asked Questions
What is the difference between helper and tender springs?
A helper spring is light and only keeps the main spring seated at droop. It is usually squeezed flat at ride height. A tender spring has more rate and gives a dual-rate feel before it goes solid. Some shops use the two words for the same part, so ask about the rate.
Do helper springs change ride height?
They take up some length in the spring stack, so adding or removing one can shift height. Measure before and after. On full-length kits, you can correct it at the lower mount. Then align the car, because height changes alter camber and toe.
Does a helper make the ride stiffer?
No. At ride height a helper is usually compressed flat, so the main spring does the work. Helpers have minimal effect on the main spring's rate. A tender spring is different, because it adds a softer first stage.
Why is my coilover spring loose when the car is jacked up?
The damper extends further than the spring's free length, and the spring has little or no preload. That is common on lowered cars. A helper spring keeps it seated. Check that the locking collar and perch are tight while you are there.
Can I just add preload instead of a helper?
Sometimes. On a full-length kit, you can add a little preload at the perch and reset height at the lower mount. On a perch-only kit, more preload raises the car, so a helper is often the cleaner fix.
Are helpers safe for street use?
Yes, when they match your main spring's inner diameter and sit on the right adapter. They are common on street and track coilovers. Inspect them when you check your collars, and replace any that are bent or cracked.
Which helper spring do I need?
Match the inner diameter of your main spring and pick a light rate meant to keep it seated. Call 1-800-460-9106 with your kit details and we will help you pick one.
Loose Spring or Odd Clunk at Droop?
Tell us your kit, your ride height and what you see when the car is on stands. We will tell you whether you need a helper, more preload or something else.
Call 1-800-460-9106 with your VIN. We carry BC Racing, KW, Fortune Auto, TEIN, Öhlins and Swift Springs, and we know how each one sets up its springs. Free shipping across Canada on most kits.
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