Thrust and Tapered Roller Bearings: Matching Axial and Radial Loads in Gearboxes and Axles

Power transmission systems rarely operate under pure radial load. Gearboxes, wheel hubs, differentials and heavy-duty axles all generate significant axial forces as well as radial forces, and the bearings must be selected accordingly. Thrust bearings carry axial load in one or both directions, while tapered roller bearings handle combined radial and axial loads in a single assembly. At FIJ, we supply a complete range of precision thrust bearings and tapered roller bearings for automotive, industrial gearbox and heavy-duty axle applications. This article explains the main bearing types, their operating principles, and how they are applied in gearboxes, axles and wheel ends.

Understanding axial and combined loading

Radial loads act perpendicular to the shaft axis, while axial loads act parallel to it. In many machines, the two occur together. Helical and bevel gears in gearboxes create both radial separating forces and axial thrust forces. Vehicle wheels transmit radial loads from vehicle weight and cornering forces, plus axial loads during braking and turning. A bearing arrangement must therefore be designed to support the combined load vector, manage thermal expansion, and maintain correct internal geometry.

Thrust bearings: carrying axial load efficiently

Thrust bearings are designed primarily to support axial loads. They are classified by rolling element geometry and load direction.

Thrust ball bearings

Thrust ball bearings consist of balls supported in a cage between shaft and housing washers. They are suitable for moderate axial loads at relatively high speeds. Single-direction thrust ball bearings carry axial load in one direction only, while double-direction designs use a central shaft washer and two housing washers to carry axial load in both directions. Because thrust ball bearings cannot support radial loads, they are usually combined with a radial bearing. Common applications include vertical pump shafts, screw jacks and small gearbox shafts.

Thrust cylindrical roller bearings

Thrust cylindrical roller bearings use short cylindrical rollers arranged radially between flat washers. They offer very high axial load capacity but are limited to low and moderate speeds because roller sliding occurs at the outer diameter. These bearings are often used in heavy press screws, machine tool spindles, rolling mills and large gearbox thrust positions. At FIJ, we supply thrust cylindrical roller bearings with machined brass cages and optimised roller profiles to reduce edge stress and improve lubricant film formation.

Thrust spherical roller bearings

Thrust spherical roller bearings combine high axial load capacity with the ability to accommodate misalignment. The barrel-shaped rollers operate on a spherical raceway, so the bearing can tolerate shaft deflection and housing bore inaccuracies. This makes them ideal for crane hooks and slew drives, pulp and paper machines, drilling rigs and mud pumps, and large industrial gearboxes with flexible housings. Thrust spherical roller bearings can also accept a proportion of radial load.

Tandem thrust bearings

When axial loads are extremely high and space is restricted, tandem thrust bearings provide a compact solution. These assemblies use multiple rows of cylindrical or tapered rollers stacked in the same direction, so the load is shared by several rolling element sets. Tandem thrust bearings are used in directional drilling equipment, extruder gearboxes, heavy thrust positions in steel and mining machinery, and large vertical pumps. Lubrication design is critical, as all rows must receive adequate oil flow to prevent overheating.

Tapered roller bearings: combined radial and axial loads

Tapered roller bearings are perhaps the most widely used solution for combined load conditions. The rollers are conical and the raceways are angled so that all roller conical surfaces converge at a common point on the bearing axis. This design ensures pure rolling motion and allows the bearing to support both radial and axial loads simultaneously.

Single row tapered roller bearings

A single row tapered roller bearing carries axial load in one direction only. Because the inner and outer rings are separable, mounting is straightforward, and the clearance or preload can be adjusted during assembly. Single row tapered roller bearings are used in vehicle wheel hubs, gearbox shafts, construction and agricultural machinery, and railway axles. By controlling the axial position of the inner ring relative to the outer ring, engineers can optimise the bearing for stiffness, life or speed.

Double row tapered roller bearings

Double row tapered roller bearings consist of two tapered roller rows arranged back-to-back or face-to-face. They provide higher radial and axial load capacity than single row bearings and can locate the shaft axially in both directions. The integrated design reduces mounting errors and saves space compared to two separate single row bearings. These bearings are common in heavy gearboxes, large axle boxes, crane trolleys and rolling mill roll necks where combined loads are high and shaft positioning must be precise.

Paired tapered roller bearings

Instead of a factory-built double row bearing, two single row tapered roller bearings can be mounted as a paired set. Back-to-back (DB) arrangements give wide separation between load centres, good moment stiffness and reduced sensitivity to misalignment. Face-to-face (DF) arrangements have closer load centres, better accommodation of misalignment and slightly lower moment stiffness. Tandem (DT) arrangements have both bearings facing the same direction to share axial load in one direction for maximum capacity. Paired arrangements are widely used in gearboxes, wheel hubs and machine tool spindles because they allow the designer to tune stiffness, capacity and mounting geometry.

Application in gearboxes

Gearboxes are among the most demanding applications for thrust and tapered roller bearings. Helical, bevel and hypoid gears generate complex load spectra with both radial and axial components.

Helical and bevel gear shafts

On helical gear shafts, the helix angle creates an axial thrust proportional to torque. This thrust must be supported by a locating bearing, often a tapered roller bearing or a paired angular contact bearing, while the other end of the shaft uses a non-locating bearing to allow thermal expansion. Four-point contact ball bearings may also be used as pure thrust bearings in high-speed gearbox designs.

High-speed and low-speed shafts

High-speed gearbox input shafts tend to use angular contact ball bearings or cylindrical roller bearings combined with thrust ball bearings, depending on axial load magnitude. Low-speed output shafts, which see higher torque and heavier radial loads, are more likely to use tapered roller bearings or spherical roller bearings. In heavy-duty industrial gearboxes, double row tapered roller bearings are often selected for the output shaft to handle combined loads and provide axial location in both directions.

Tandem thrust in extruder and pump gearboxes

Extruder gearboxes and large pump drives can generate extremely high axial thrust. Tandem thrust bearings, often using cylindrical rollers, distribute this thrust across multiple rows. Careful attention to oil flow and cooling is needed to prevent thermal runaway in these heavily loaded positions.

Application in wheel hubs and axles

Wheel bearings must support vehicle weight, cornering forces, braking torque and road impacts, all while operating in a contaminated environment. Tapered roller bearings dominate this market because of their combined load capability and adjustable preload.

Wheel hub bearings

Modern wheel hub units often integrate two rows of tapered roller bearings, seals, and a flange for brake rotor or wheel attachment into a single pre-assembled and pre-adjusted unit. These compact assemblies simplify assembly, reduce weight and improve reliability. For heavier commercial vehicles and off-highway equipment, larger single row or paired tapered roller bearings are still common. Preload is critical: too little preload causes looseness, wheel wobble and fatigue; too much preload increases friction, heat and wear.

Differential bearings

The differential in a driven axle uses tapered roller bearings to support the differential case and gearset. These bearings must handle the radial loads from gear mesh forces and the axial loads created by the bevel gear thrust. Correct preload of the differential bearings is essential to maintain gear mesh pattern and prevent noise, overheating and premature gear failure.

Heavy-duty axle bearings

Heavy-duty axles in trucks, buses, construction machinery and railway vehicles require bearings with very high load capacity and resistance to shock. Tapered roller bearings, spherical roller bearings and cylindrical roller bearings are all used depending on the axle design. Multi-row tapered roller bearing arrangements are common in railway axle boxes because they can handle high radial loads and provide the axial guidance needed for curve negotiation.

Preload, clearance, lubrication and sealing

The internal clearance or preload of thrust and tapered roller bearings has a direct effect on stiffness, life, noise, temperature and running accuracy. Excessive clearance reduces stiffness and can cause vibration and noise. Insufficient clearance increases friction and heat, shortening lubricant and bearing life. In tapered roller bearings, clearance is adjusted by controlling the axial position of the inner ring on the shaft.

Preload is a deliberate negative clearance that removes all internal play. Preloaded bearings have higher stiffness and better positional accuracy, making them ideal for machine tools and precision gearboxes. However, preload increases friction and must be carefully controlled to avoid overheating. Common preload methods include shim selection during assembly, nut adjustment with torque or position control, spacer grinding for precision matched sets, and factory-set preload in sealed hub units. In automotive wheel bearings, preload is usually set during manufacture and should not be disturbed.

Thrust and tapered roller bearings in gearboxes and axles operate under high contact stress. At FIJ, our bearings are manufactured from clean bearing steel with controlled heat treatment to optimise hardness, fracture toughness and dimensional stability. Gearboxes are usually lubricated by splash or circulating oil, which also feeds the bearings, while axle and wheel hub bearings may use high-performance greases with EP additives. Wheel hub and axle bearings are exposed to water, dust, road salt and debris, so effective sealing is essential.

Selection guidelines

When selecting thrust or tapered roller bearings for a gearbox or axle application, calculate the equivalent dynamic load, select a bearing with adequate basic dynamic load rating, check the static safety factor, choose the correct locating or non-locating arrangement, decide between single row, double row, paired or tandem configurations, and specify preload or clearance based on stiffness, speed and temperature requirements.

FIJ provides technical support and custom bearing solutions to help engineers navigate these decisions. From standard catalogue products to application-specific designs, we deliver bearings that match the real demands of gearboxes, axles and wheel ends.

Conclusion

Matching axial and radial loads in gearboxes and axles requires a clear understanding of thrust bearings, tapered roller bearings and the interaction between load, speed, stiffness and thermal expansion. Thrust ball bearings, thrust cylindrical roller bearings, thrust spherical roller bearings and tandem thrust bearings each have a role in carrying axial load. Single row, double row and paired tapered roller bearings offer flexible solutions for combined radial and axial loads.