Radius Arm with Fitting Position Front, Rear for 2017 BMW M2 Base

A radius arm runs fore and aft rather than across your BMW M2, holding the wheel against everything braking and acceleration apply to it. On a strut front end it works alongside the lower control arm, which handles the sideways loads while the radius arm handles the lengthwise ones.

Between them they locate the bottom of the strut, and the radius arm is the one that decides whether your front end stays put when you use the brake pedal.

The BMW M2 Arm That Holds the Wheel Against Braking Load

When you brake hard, the entire car tries to push the front wheels rearward. The lower control arm cannot resist that, because it runs across the car rather than along it, so the load lands almost entirely on the radius arm.

There is nowhere else for it to go. No second arm sharing the job, no wishbone spreading it across two pivots, just one link and the bushing at the end of it taking the full fore and aft reaction of every stop you make.

Because the arm acts as a lever, whatever it allows gets multiplied by the time it reaches the tire. The wheel moves rearward under braking, caster changes while it does, and the front end goes vague and floaty at exactly the moment you were asking it to be precise. Turn in suffers for the same reason, since the wheel is being asked to change direction while its fore and aft position is still settling.

Two Very Different Parts Share This Name

Worth clearing up before you order anything, because the terminology causes genuine confusion and the two parts have nothing in common.

On the strut front ends this range covers, the same component is called a radius arm, a radius rod, a tension rod, a strut rod or a compliance arm depending on who built the car and who wrote the catalog. A strut rod and a radius arm are the same thing here.

Separately, a solid front axle truck also has radius arms, running from the axle housing back to the frame and controlling how far the housing rotates. Those live on a completely different type of suspension, they are a much larger component, and nothing on this page applies to them.

Check what your BMW M2 actually has before ordering, because a search for radius arms returns both and the parts are not interchangeable in any way.

BMW M2 Radius Arm or Just the Bushing?

Both are legitimate purchases and the right answer depends on what has actually failed.

A radius arm bushing or strut rod bushing on its own is the answer when the arm is straight, the mounting eye is round and the ball joint or outer end is sound. That covers the majority of cases, because the bushing is what wears and the arm itself is a fairly simple piece of metal that usually outlasts it.

The complete arm is the answer when the arm is bent, when corrosion has eaten into it, when a mounting eye has worn oval and will no longer hold a bushing properly, or when the outer joint has gone on a design that integrates one. It is also the answer when you would rather not spend an afternoon at a press, since an assembled arm turns the job into a bolt-in.

Check the eye before committing to a bushing. A bore that has gone oval will not seat a new bushing correctly, and finding that out after pressing one in means doing the work twice and paying for it twice.

Caster Built Into the BMW M2 Arm

Some arms in this range are not straight replacements.

Because the radius arm sets the fore and aft position of the wheel, moving that position changes caster. Arms and bushings with a double offset built in shift the pivot deliberately, adding positive caster rather than simply restoring what the factory gave you.

More caster means stronger self centering, better stability at speed, and more negative camber gain as you turn the wheel, which puts the outside front tire at a better angle exactly when it is loaded hardest. That is why caster correction turns up on almost every serious street and track build rather than only on cars that have drifted out of alignment.

Because the offset is directional, it can also be set to correct one side differently from the other. On a car that pulls steadily with tires and pressures ruled out, that is often the only practical fix available.

What a Worn BMW M2 Radius Arm Feels Like

• A front end that feels vague or floaty under braking
• The car squirming or moving around when you brake from speed
• Delayed turn in, where the car takes a moment to respond to steering input
• A clunk or thud from the front under braking or on take up of drive
• Uneven tire wear that keeps returning after every alignment
• Caster reading low or uneven on an alignment printout
• Visible cracking, splitting or material squeezed out at the bushing
• Rubber that has separated from its metal sleeve, which is common in this position
• A bent or visibly damaged arm after hitting something hard

The braking symptom is what separates this from everything else. Worn control arm bushings announce themselves over bumps, worn ball joints announce themselves when the wheel is turned, and a worn radius arm shows up when you use the brakes, because resisting that load is the job it exists to do.

Separators, Orientation and Torque at Ride Height on Your BMW M2

Support the car properly and take the load off the suspension before releasing either end of the arm.

Where the arm attaches through a ball joint, use a proper separator rather than a hammer, since hammering damages the knuckle bore and the stud threads on components that cost considerably more than the tool.

Where you are pressing a bushing rather than fitting a complete arm, use a correct diameter press tool and check the eye once the old bushing is out. Improvising with sockets or bearing shells is how arms get ruined, and the arm is the expensive part of this job.

Pay close attention to orientation on any offset bushing or arm. Fitted the wrong way round it moves caster in the opposite direction to the one you wanted, which leaves the alignment further out than when you started and is easy to do halfway through a job.

Torque with the car on its wheels at ride height rather than hanging at full droop. This matters more here than at most positions, because the arm sits under constant fore and aft load and a bushing clamped in the wrong position spends its whole life twisted and binds from the first mile.

Do both sides and then get an alignment, because fitting these changes caster immediately, and the alignment is what confirms the two sides now match each other rather than pulling against one another.

Find Radius Arms for Your BMW M2

Radius arms sit within our control arms lineup, and C-bushings tune caster on solid-axle trucks.

Select your BMW M2 to see the radius arms and radius arm bushing kits available for it, in standard and double offset caster specifications. Every Whiteline component is backed by our warranty, a fitment guarantee and 60 day returns.