Control Arm & Radius Arm Kits

On a lot of front ends the lower suspension is not one arm but two. A control arm holds the wheel in its lateral position and a radius arm holds it fore and aft, and between them they set camber and caster.

These kits supply both, as a matched set of two control arms and two radius arms, so the entire lower end of the front suspension is replaced and corrected together.

Two Arms, Two Angles

Each arm governs a different axis, which is why they are sold as a pair.

The control arm sets how far the bottom of the wheel sits in or out, so it governs camber. The radius arm, sometimes called a caster arm or a radius rod depending on the vehicle, sets how far forward or back the wheel sits, so it governs caster. Neither can do the other's job.

They also work against each other constantly. Under brakes the radius arm takes the fore and aft load while the control arm resists the wheel being pushed sideways, and the two have to stay in a fixed relationship for the geometry to hold. That is the whole reason the pairing matters.

Why Half a Job Stays Half a Job

Replace one arm and leave the other and you have corrected half the geometry while the other half is still deflecting under load.

It is worse than that in practice. A new arm with fresh bushings is rigid, and the old arm beside it still flexes, so the two ends of the lower suspension now move by different amounts under the same input. The geometry shifts every time you brake or turn in, and the alignment you just paid for is only correct while the car is standing still.

Doing both at once removes that mismatch and it removes a second trip to the aligner.

Adjustment Built Into the Bushings

The kits use adjustable synthetic elastomer bushings rather than fixed ones, which is what turns a replacement into a correction.

Camber and caster are adjusted separately, typically to around half a degree either way on each, which is enough to bring a lowered car back into specification or to dial in a performance alignment deliberately. On some kits the radius arms carry offset bushings for caster adjustment, and others use a left and right hand thread turn buckle so the length can be set on the car with a spanner rather than taken apart.

Because each side adjusts independently, the kits also fix problems a symmetrical correction cannot. A car that has settled unevenly, or one that pulls with tyres and pressures ruled out, gets corrected side to side rather than split down the middle.

Low compliance bushings are used throughout to hold position under load while keeping noise and vibration in check, since the point of the exercise is precision rather than punishment.

Lowered Cars and Where the Geometry Goes

Most of the demand for these kits comes from two places, and they often arrive together.

Higher performance cars work their front control arm and radius arm bushings hard. The original rubber takes a beating, has a limited service life, and once it perishes the geometry starts wandering under load even though the static numbers still read correctly.

Then there is ride height. Fit lowering springs or coilovers and the arms swing through a different part of their arc, so camber goes negative and caster washes off. On plenty of platforms the car ends up outside specification with nothing worn at all, and there is no factory adjustment left to recover it.

A kit addresses both at once. Fresh arms remove the deflection, and the adjustable bushings hand the aligner the range that was never there to begin with.

Arms or Just the Bushes

Worth deciding properly before you spend, because the cheaper route is sometimes the right one.

Control arm bushes on their own make sense when the arms are straight, the mounting eyes are round, the ball joints are tight and ride height has not changed. Fresh front lower control arm bushes will remove the deflection and stop the geometry moving while you drive. Front radius arm bushings in a double offset caster design will even give you some correction without changing the arm.

The kit is the better purchase when you want camber and caster correction together, when the arms themselves are tired or damaged, when a mounting eye has worn oval and will no longer hold a bush, or when you simply want it done once. The arms have to come off the car for either job, so the labour is the same either way, and by the time both ends are due the complete set frequently works out better value.

Signs You Need a Set

• Steering that feels lazy or imprecise in the first part of its travel
• The front end squirming or wandering under heavy braking
• A delay between turning in and the car taking a set
• Uneven tyre wear across one edge that keeps returning after alignment
• An alignment the shop cannot bring into specification with what the car provides
• Camber or caster reading out of range on the printout after lowering
• A steady pull to one side that tyres and pressures do not explain
• Clunking from the front over bumps or on take up of drive
• Cracked, split or squeezed out bushing material at the inner mounts

That fifth one is the clearest signal of the lot. If the aligner has run out of adjustment, no amount of new rubber will give it back.

Fitting and Alignment

Both arms bolt into the factory mounting locations and arrive assembled, so this is a spanner job rather than press work.

Fit both arms on a side before moving on, and do both sides. Half a kit on one corner gives the front end two different rates of movement and the car will pull under brakes regardless of what the alignment says.

Torque everything with the car on its wheels at ride height rather than hanging at full droop. Whatever position a bushing is clamped in becomes its neutral position, so an arm torqued at droop spends its life twisted and binds from the first kilometre.

Book the wheel alignment for the same visit, because the entire purpose of these kits is to give the aligner range and a stable platform to set the geometry against. On kits with on car adjustment, set them roughly beforehand and let the aligner make the final call with the machine reading the numbers. Camber first, then caster, and tell them what the car is used for since a street alignment and a track alignment are different targets.

Find Kits for Your Vehicle

Need individual arms? They're in our suspension arms range.

Select your vehicle to see the control arm and radius arm kits available for it, and check each listing for the adjustment range it offers and whether the arms adjust on the car. Every Whiteline component is backed by our warranty, a fitment guarantee and 30 day returns.