The short version
- Three element shapes exist, and each is a different answer to one problem.
- A cornering wheel is pushed sideways, and that is what separates them.
- Tapered rollers dominated for eighty years because they handle both loads at once.
- Two rows of balls set at opposing angles then beat them, and that is why your car has no adjustment.
Types of wheel bearings sounds like a taxonomy question. It is really a question about one force.
A wheel carries weight downward, which is easy. It also gets pushed sideways every time the car turns, and that load decides the design.
The two loads
Everything below follows from the difference between them.
| Load | Direction | When |
|---|---|---|
| Radial | Straight down through the wheel | Always, from the vehicle’s weight |
| Axial or thrust | Sideways along the axle | Every corner, every camber change |
In a firm corner the outside wheels take the transferred weight and a substantial sideways push at once.
A bearing that handles weight well and sideways force poorly is no use on a car, whatever its radial rating says.
The three shapes
Balls touch the raceway at a point. That gives very low friction, since a point has almost nothing to scrub.
It also limits load, since the force passes through a patch smaller than a pinhead. A plain radial ball bearing handles sideways load poorly.
Straight rollers touch along a line instead. Far more contact area, so far more radial capacity for the same size.
Their weakness is the same axis. A cylindrical roller resists nothing sideways, so it is a poor choice where cornering matters.
Tapered rollers touch along an angled line. Because that contact is inclined, a sideways push resolves into the raceway rather than sliding the roller out.
Why tapered rollers ruled for so long
That angled contact is genuinely elegant, and it solved the car problem for most of the twentieth century.
Fitted in opposing pairs, two tapered rows carry weight and cornering load together, and the pair adjusts to remove all play.
They remain standard on trailers, older vehicles and heavy equipment. The trailer section covers why that application never moved on.
Adjustment. A tapered pair must be set to a specific clearance, and that setting drifts as things bed in and wear.
So it demands periodic service. Fine on a trailer you already inspect annually, a nuisance on a family car.
What replaced them
Why the replacement uses two opposed rows is on the double row page.
The answer that won is less obvious than it looks.
Take two rows of balls and set their contact lines at opposing angles. Each row now has an inclined contact, exactly like a tapered roller, resisting sideways load one way.
Together they handle cornering both ways, while keeping the low friction of point contact. That is the design behind most modern types of wheel bearings.
Better still, the maker sets the clearance during assembly and seals it in permanently. No adjustment on the vehicle, ever.
The angular contact ball design made a pre-set, sealed, maintenance free hub possible.
Everything else about modern hubs, including why they are replaced rather than serviced, follows from that one geometric trick.
Which one you have
| If you see | It is |
|---|---|
| Castle nut and cotter pin | Adjustable tapered pair |
| Large single use nut, bolted flange | Sealed angular contact ball unit |
| Cone that lifts out in your hand | Tapered roller |
| Sealed ring pressed into the knuckle | Double row ball, usually |
The practical consequences of each are on the design comparison, which also covers the generation numbering applied to them.
Where each still wins
None of these designs is obsolete. They occupy different jobs.
Tapered rollers win where loads are high, service is expected anyway and adjustment is acceptable. Trailers, trucks and industrial equipment.
Angular contact balls win on passenger cars, where low friction and sealed assembly matter more than ultimate capacity.
Straight rollers rarely appear at a wheel at all, because pure radial loading is not what a wheel experiences.
A note on generations
Worth separating from element shape, because the two get conflated.
Generation numbering describes how much of the assembly is integrated, not the shape of the rolling elements. A first generation part is a bearing alone. A third has two flanges and usually an encoder.
A generation three unit almost always contains angular contact balls, but the number describes the packaging rather than the bearing type.
How loosely that term gets used by sellers is on the brands page.
Timken built its reputation on the tapered roller design, as the Timken page covers.
Small machines take this further and often skip rolling elements altogether, as the page on mower wheels and bushings explains.
Common questions
What are the main types of wheel bearings?
The types of wheel bearings divide by element shape into ball, straight roller and tapered roller. On vehicles you meet tapered roller pairs and sealed angular contact ball units.
Why did tapered rollers get replaced on cars?
Because they need periodic adjustment. Angular contact ball designs can be pre-set and sealed at the factory, which removed vehicle maintenance entirely.
Are ball bearings weaker than roller bearings?
For pure radial load, yes, because point contact carries less than line contact. Angular contact ball designs compensate by handling sideways load well.
What is angular contact?
A ball bearing where the contact line between ball and raceway is inclined rather than straight across. That inclination lets it resist sideways load.
Why do trailers still use tapered rollers?
High load capacity, low cost, and the design’s need for adjustment is not a problem on something already inspected and repacked annually.
Does the type change how it fails?
The mechanisms are the same across types. What differs is whether you can inspect it, since a sealed unit hides everything until it makes noise.
Is generation the same as type?
No. Generation describes how much of the hub is integrated into the part. Type describes the shape of the rolling elements inside it.