Tapered Roller Bearings

What is a tapered roller bearing?

A tapered roller bearing is a rolling bearing that uses cone-shaped (tapered) rollers running between tapered inner and outer raceways. The raceways and rollers are angled so that, if their lines were extended, they would all meet at a single point on the bearing axis. This geometry makes the rollers roll true without skidding, and lets the bearing carry heavy radial and axial loads at the same time.

A standard bearing has four main parts:

• An inner ring, called the cone, which fits onto the shaft
• An outer ring, called the cup, which sits in the housing
• A single row of tapered rollers
• A cage that keeps the rollers evenly spaced.

The cone, rollers, and cage are held together as one unit, called the cone assembly.

• The cup is separate, so the cone assembly and cup can be fitted independently.
• This makes mounting easier and lets the clearance or preload be set when the bearing is fitted.

Because the rollers are set at an angle, a single tapered roller bearing carries axial load in one direction only. For this reason, they are almost always used in pairs, facing each other, so the shaft is located in both directions. Rings and rollers are usually made from hardened chrome steel (grade 52100) or case-hardened steel. Cages are most commonly pressed steel, with polyamide and machined brass also available.

Why are tapered roller bearings essential?

They carry heavy combined radial and axial loads in a compact space, which makes them the default choice for wheels, gearboxes, and any shaft that has to resist both types of load at once. Line contact between the rollers and raceways gives them high load capacity and stiffness. Because the clearance or preload is set during fitting, a pair of tapered roller bearings can be adjusted to give a very rigid, accurate shaft.

They are separable, which makes them easy to fit, inspect, and replace. Their boundary dimensions are standardised internationally. So a bearing of a given reference has the same bore, outer diameter, and width, regardless of which reputable manufacturer makes it.

Typical applications include:

• Car, van, and trailer wheel hubs
• Truck and agricultural axles
• Gearboxes and differentials
• Industrial gear drives
• Machine tool spindles
• Rolling mills
• Pumps and compressors
• Conveyor and crusher drives
• Construction and mining equipment
• Rail axleboxes

The main types of tapered roller bearings

• Single-row tapered roller bearings - These are the standard design and by far the most common. They carry radial load and axial load in one direction, and are usually fitted in pairs.
• Matched pairs - Two single-row bearings supplied as a matched set, ready to fit with a set clearance or preload. They can be arranged face-to-face (DF), back-to-back (DB), or in tandem (DT).
• Double-row tapered roller bearings - These have two rows of rollers in one unit, with either a double cup and two cones, or a double cone and two cups. They carry axial loads in both directions and are used in gearboxes, rolling mills, and wheel units.
• Four-row tapered roller bearings - Used for the very heavy radial loads in rolling mill roll necks.
• Steep angle tapered roller bearings - These have a larger contact angle, so they carry higher axial loads compared to radial loads. They are used where the axial load is high, such as in worm gear drives and pinion shafts.
• Flanged cup bearings - These have a flange on the outer ring, which locates the bearing axially in the housing without a shoulder.
• Metric and inch bearings - Metric bearings follow ISO numbering, such as 30205. Inch bearings are sold as separate cone and cup part numbers, such as LM11949 and LM11910, or as a matched set.

Cage variants include:

• Pressed steel cages - Strong, cost-effective, and the standard choice in most sizes.
• Polyamide cages - Light and quiet, but typically limited to around 120°C in continuous use.
• Machined brass cages - Very robust, used in larger sizes and heavy-duty or high-temperature applications.

How to choose the right tapered roller bearing?

• Size and dimensions - The bore must suit the shaft; the outer diameter and width must fit the housing. For the same bore, a heavier dimension series has a larger outer diameter, larger rollers, and higher load capacity, but takes up more space.
• Load - Work out the radial and axial loads and whether they are steady or involve shocks. Compare them with the bearing’s basic dynamic load rating and basic static load rating, which are published in manufacturers’ catalogues. Remember that radial load on a tapered roller bearing creates an internal axial force, which must be taken by the opposing bearing.
• Contact angle - A standard contact angle suits most combined loads. Choose a steep angle series where the axial load is high compared to the radial load.
• Arrangement - Choose face-to-face or back-to-back mounting. Back-to-back gives greater stiffness against tilting, while face-to-face is more tolerant of misalignment.
• Clearance or preload - Tapered roller bearings are adjusted during fitting, usually with a nut, shims, or spacers. A small clearance suits most general applications, while preload is used where maximum stiffness and accuracy are needed.
• Lubrication and environment - Grease suits most wheel hubs and general machinery, while oil suits higher speeds and gearboxes. Tapered roller bearings are usually open, so sealing must be provided by the housing.

Essential references and specialised ranges

How the numbering works:

The first digit, 3. Identifies a metric tapered roller bearing.

The next two digits indicate the dimension series: 302 is light, 303 is medium, 313 is a steep angle series, 320 and 329 are thin-section series, 322 and 323 are wider series, and 330, 331 and 332 are wide series.

The last two digits indicate the bore:

00 = 10mm, 01 = 12mm, 02 = 15mm, 03 = 17mm

From 04 upwards, multiply by five (for example, 30205 = 25mm and 32210 = 50mm)

Inch bearings use a different system, with separate part numbers for the cone and the cup. The letters at the start show the load class, from light (such as LL and L) to heavy (such as HM and H). For example, LM11949 is a cone and LM11910 is the matching cup.

Suffixes:

J2 = pressed steel cage

Q = optimised contact geometry and surface finish

A = modified internal design

XL = X-life series with higher performance

HR = high-capacity design, used as a prefix

DF = matched pair, face-to-face

DB = matched pair, back-to-back

DT = matched pair, in tandem

Tapered roller bearings do not usually have internal clearance classes like C3, as the clearance is set during fitting.

Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.

FAQ - All you need to know about tapered roller bearings

What is the difference between a cone and a cup?

The cone is the inner ring, which comes with the rollers and cage fitted as one assembly. The cup is the outer ring. On inch bearings, the cone and cup are sold under separate part numbers, so make sure both parts match.

Why are tapered roller bearings fitted in pairs?

A single tapered roller bearing only carries axial load in one direction. Fitting two bearings facing each other lets the shaft be located in both directions, and allows the clearance or preload to be set between them.

Can tapered roller bearings tolerate misalignment?

Only to a very small degree. Misalignment overloads the ends of the rollers, causing heat, wear, and early failure, so shafts and housings should be accurately aligned.

Do tapered roller bearings need lubrication?

Yes, lubrication separates the rollers from the raceways and the guide flange, reduces friction, and protects against corrosion. Wheel hub bearings are usually grease-packed, while gearbox bearings are usually oil lubricated.

Click here to learn how to maintain a bearing.

Can I replace a tapered roller bearing myself?

In many cases, yes. Fit the cup into the housing and the cone assembly onto the shaft separately, pressing only on the ring being fitted. Always replace the cup and cone together, as a new cone in a worn cup will fail early. Once fitted, adjust the clearance or preload to the manufacturer’s or vehicle maker’s specification, while turning the shaft to seat the rollers. Never strike the bearing directly with a hammer.

How do I identify a bearing I need to replace?

The reference is usually marked on the side face of the cone and the cup. If the markings are worn away, measure the bore of the cone, the outer diameter of the cup, and the overall width with callipers and match them against a size chart. On inch bearings, check the cone and cup part numbers separately.

Click here to learn how to measure a bearing.

How can I tell if a bearing is worn or failing?

Warning signs include:

• Grinding, rumbling, or humming noises
• Increased vibration
• Rough or uneven rotation
• Play in the shaft or wheel
• Overheating
• Discoloured, pitted, or flaking raceways on the cup or cone

Click here to learn how to recognise a failing bearing and tips on how to extend the life of bearings.