The short version
- Six parts, and the clearest way to learn them is to follow the load from road to chassis.
- Only a few rolling elements at the bottom carry the weight at any moment. The rest are along for the ride.
- The cage carries no load at all, which is why people misjudge what it does.
- Cone and cup, inner and outer race, are the same two parts under different names.
Diagrams of wheel bearing parts label everything and explain nothing. You end up knowing six words and little else.
A better route is to trace the load. Follow the car’s weight from the tire contact patch up into the suspension, and each component explains itself.
Wheel bearing parts, following the load path
Start at the road and work inward.
| Step | Component | What it does with the load |
|---|---|---|
| 1 | Wheel and studs | Bolts to the hub flange |
| 2 | Hub flange | Turns with the wheel, carries the studs |
| 3 | Inner race, or cone | Rotating ring the elements run on |
| 4 | Rolling elements | Balls or rollers, the actual bearing |
| 5 | Outer race, or cup | Stationary ring, held in the knuckle |
| 6 | Knuckle | Passes the load into the suspension |
Inner race and cone mean the same thing. Outer race and cup mean the same thing. Tapered roller literature prefers cone and cup, ball literature prefers races.
Nothing turns on the difference, but catalogs mix the terms freely and that causes real confusion when ordering wheel bearing parts.
The part that surprises people
Only a handful of the rolling elements are doing anything at any given moment.
The load runs downward through the bearing to the road, so it is carried by the elements at the bottom of the race. The ones at the top are unloaded and simply traveling round.
Each element enters the loaded zone, takes its share, and leaves again, several times per wheel revolution.
That is why bearing life is counted in revolutions rather than miles. It is also why load has such a violent effect, being cubic, as the lifespan page shows.
What the cage actually does
The cage, sometimes called the retainer, is the component people most often misread.
It carries none of the load. Take it out and the bearing would still support the car, briefly.
Its job is spacing. Without it the rolling elements drift together, bunch up and rub rather than rolling cleanly.
Two rolling elements touching are moving in opposite directions at the contact point, so they scrub rather than roll.
That generates heat exactly where the grease is working, which is why a broken cage destroys a bearing quickly despite never carrying load.
The surfaces that matter
Everything in the assembly is ordinary steel except three surfaces, and those are exceptional.
Both raceways and the surface of every rolling element are hardened, ground and polished to a finish measured in fractions of a micron.
They never touch in normal running. A film of oil under a micron thick separates them, and that film is the entire mechanism.
Which is why one particle of grit is serious. It is many times thicker than the film protecting the steel, so it cannot pass without damaging something.
What a bearing actually looks like
Useful if you are trying to identify one on a car rather than in a diagram.
A sealed hub unit looks like a metal disc with studs on one face and a bolt flange on the other. You cannot see any bearing, because it is inside.
A pressed-in bearing looks like a thick steel ring, roughly the diameter of a coffee mug, with a rubber seal face on each side.
A tapered roller bearing looks like a cone of angled rollers held in a cage, and it comes apart in your hand into cone and cup.
Which you have changes every practical question, and the design comparison settles it in a minute with the wheel off.
The parts that are not the bearing
Four things appear in wheel bearing parts diagrams that belong to the assembly rather than the bearing itself.
The seal, which retains grease and excludes water. It is where most failures actually start, and the seals page covers it properly.
The ABS encoder, a ring of magnetic poles or teeth that gives the wheel speed signal.
The snap ring, a backstop limiting travel on pressed-in applications. It does not hold the bearing in.
The dust cap, which keeps the worst of the road out of the outer end.
Why the terminology is such a mess
Worth a short explanation, since it causes ordering mistakes.
Wheel bearing, hub, hub assembly and hub bearing get used interchangeably by retailers, and they do not all mean the same thing.
Strictly, the bearing is the rolling assembly. The hub is the flanged part carrying the studs. A hub assembly is both, pre-built as one sealed unit.
When ordering, ignore the words and match the part number, which the vehicle identification page explains how to do.
Common questions
What are the parts of a wheel bearing?
The wheel bearing parts are an inner race, an outer race, rolling elements, a cage, seals, and on modern units an integrated ABS encoder. The flange and studs belong to the assembly.
What is the difference between a cone and a cup?
None beyond naming. A cone is the inner race and a cup is the outer race. Tapered roller catalogs prefer those terms.
Do all the balls carry weight?
No. Only those in the loaded zone at the bottom carry the car at any moment, and each element passes through that zone several times per revolution.
What does the cage do?
It spaces the rolling elements. It carries no load, but without it they bunch together and rub, generating heat that destroys the bearing.
Do the metal surfaces touch?
Not in normal running. An oil film under a micron thick separates them, which is also why a speck of grit does so much damage.
What does a wheel bearing look like?
A sealed hub looks like a metal disc with studs on one face. A pressed-in bearing looks like a thick steel ring with rubber seal faces. A tapered set comes apart into cone and cup.
Is the hub part of the bearing?
Not strictly. The hub carries the studs and the bearing carries the load, though a sealed unit builds them as one part.