Ball joints are classified into two functional types: load-carrying joints, which support part of the vehicle's weight, and follower joints (also called non-load-carrying), which act only as a pivot point with no significant weight on them. Which position — upper or lower — ends up being the load-carrying one depends entirely on the suspension design, which is why "load-carrying vs. follower" and "upper vs. lower" are related but not interchangeable ways of describing the same two joints.
Load-Carrying vs. Follower: The Functional Split
- Load-carrying joint. Bears part of the vehicle's sprung weight in addition to acting as a pivot. Because it's under constant structural load as well as pivoting stress, it typically wears faster and is the more common point of failure.
- Follower joint. Handles pivoting and steering motion but carries little to no vehicle weight. It maintains suspension geometry — camber, caster, wheel alignment — rather than holding the vehicle up.
Which Joint Carries the Load Depends on Suspension Type
This is the part a straight "upper vs. lower" answer misses:
| Suspension type | Load-carrying joint | Follower joint |
|---|---|---|
| Double wishbone / SLA, spring seated on lower control arm (most common layout) | Lower | Upper |
| Double wishbone, spring seated on upper control arm (less common) | Upper | Lower |
| MacPherson strut | Lower (only joint present) | None — the strut's upper bearing mount carries the load instead |
| Solid front axle (full-size 4×4 trucks, live-axle Jeep-type platforms) | Upper and lower share the load | Doesn't apply — there's no separate control arm splitting the two roles |
That last row matters for off-road-oriented vehicles specifically: without independent control arms, a solid front axle's upper and lower joints theoretically share load rather than splitting into one carrier and one follower — a distinction most consumer-facing explanations of "the two types of ball joints" skip entirely because they're written with an independent front suspension in mind.
A Level Deeper: How Load-Carrying Joints Actually Fail
Most explanations of ball joint types stop at "load-carrying vs. follower." One further layer — covered in depth by only one source in this research, the trade publication Counterman — is worth including because it explains why load-carrying joints fail the way they do, not just that they fail first.
Load-carrying joints split further into compression-loaded and tension-loaded, depending on which direction the vehicle's weight pushes on the joint:
- Compression-loaded — the sprung weight pushes the arm and knuckle together through the joint (typical when the upper control arm carries the spring load). A failing compression-loaded joint wears itself deeper into the bearing material over time, growing looser until it self-destructs from within.
- Tension-loaded — the sprung weight pulls the joint away from the knuckle (typical when the lower control arm carries the spring load, which is the more common layout). A failing tension-loaded joint gradually pulls against the outer edge of its bearing until the stud eventually separates from the housing entirely.
Both failure modes are dangerous, but they're not identical: a compression failure tends to stay "loose but still loaded" longer, since the vehicle's weight keeps pressing the stud into the housing even as it degrades. A tension failure is more prone to a cleaner separation, since the failing direction of wear is the same direction that would pull the joint apart. This distinction is a single-source finding, not something cross-verified across multiple independent guides — but it comes from an industry technical publication rather than a general consumer source, and it's a meaningfully more precise explanation than "the lower one wears out first" without saying why.
Other Ways Ball Joints Get Classified
Beyond the functional split above, you'll also see ball joints categorized by:
- Maintenance design — sealed (pre-lubricated for life) vs. greasable (has a zerk fitting for periodic service).
- Mounting method — press-fit vs. bolt-on vs. threaded, referring to how the housing attaches to the control arm or knuckle.
These are useful distinctions when you're sourcing a replacement part, but they're not what's usually meant by "the two types" — that phrase almost always refers to load-carrying vs. follower.
Related reading: Where is a ball joint located? · How to inspect ball joints? · How to press in ball joints?
