30300 Series Tapered Roller Bearings are used for carrying heavy combined radial and axial load in one direction, always mounted in opposition to a second row and adjusted at assembly to a defined endplay or preload. The raceways and the roller are all sections of cones whose apexes meet on the bearing axis, so the roller rolls without sliding and every load is resolved down the taper — which is why the pair must be set, not merely assembled. This page sets out the industries and machine positions where the type is specified, what has to be stated on the order, mounting practice, and the duties where a different bearing type is the correct answer. Boundary dimensions are to ISO 355 / DIN ISO 355 / GB/T 297. This series is catalogued from 15 mm to 100 mm bore; the full table of boundary dimensions is further down the page.
Typical Applications for 30300 Series Tapered Roller Bearings
The machine positions and sectors where this type is specified:
- Maintenance and repair (MRO): replacing a failed bearing where the original designation, clearance group and sealing have to be matched exactly.
- OEM machine building: designed-in shaft support on new equipment, specified from the load, speed and envelope at the design stage.
- Wheel hubs: the classic opposed pair, taking vehicle weight radially and cornering load axially, set to a specified endplay at assembly.
- Pinion and differential shafts: axle drives where the hypoid gear mesh produces a large permanent axial force alongside the radial load.
- Gearboxes: shaft positions with heavy helical or bevel gear thrust, where an opposed pair takes both components in one arrangement.
How to Specify 30300 Series Tapered Roller Bearings for Your Application
- Bore: Start from the bore the shaft or housing gives you — this series is catalogued from 15 mm to 100 mm — then check the outer diameter and width against the space available. The boundary dimensions are fixed by the standard, so they are the same from any manufacturer; the load ratings and limiting speeds are not, and belong to the specific bearing being supplied.
- Assembled width T: Design the housing around the assembled width T rather than the ring widths B and C: T is the only one of the three that describes the mounted bearing.
- Contact angle and series: A steeper angle (32300, 33100 and the steep-angle inch series) carries proportionally more axial load; the shallower 30200 and 32000 series favor radial. The angle is a design property of the series, and the assembled width T rather than the ring widths B and C is the dimension the housing has to accept.
- Setting: State the required setting on the drawing and on the order: endplay, zero, or preload, with a tolerance. This is the step installers get wrong more than any other in bearing assembly — the same pair of bearings gives normal life, short life or seizure depending only on how it was set.
- Cup and cone as a set: The bearing is separable and supplied as a matched cup and cone. Order and store them as a set: cups and cones are not interchangeable between assemblies, and mixing them changes the setting by more than the tolerance on it.
- Designation and suffixes: State the complete designation including every suffix. The base number gives the type and the boundary dimensions; the suffixes carry the sealing, the cage, the clearance group, the tolerance class and any special execution — and two bearings whose base numbers match but whose suffixes differ are not interchangeable.
- Preload class: This type is specified by preload rather than by an internal clearance group, because the axial setting is made when the bearings are clamped together on assembly. State the preload class (light, medium, heavy) on the order, and state the arrangement it applies to — the preload belongs to the set, not to one bearing.
- Sealing arrangement: This type is supplied open, so the sealing belongs to the housing around it. Specify the shaft seal, flinger or labyrinth that will keep the lubricant in and contamination out — with an open bearing, the sealing arrangement, not the bearing, decides how long it survives its environment.
- Cage material: State the cage. Pressed steel is the default and suits most duties; machined brass takes shock, high temperature and poor lubrication better and is used in large and heavily loaded bearings; polyamide is quiet, light and low-friction but has a temperature limit of about 120 °C and is attacked by aged oil. The cage is not a detail — it is the component that most often sets the real temperature limit of the bearing.
- Shaft and housing fit: Specify the seat tolerances, not just the bearing. The rule is that the ring which rotates relative to the load direction takes the interference fit: for a rotating inner ring under normal radial load the shaft seat is typically k5 or k6 with the housing bore H7, and where the outer ring rotates the interference moves to the housing (N7 or P7) with a clearance fit (g6) on the shaft. Heavier loads and hollow shafts move the fits tighter. A correctly chosen bearing in the wrong fit fails anyway — too loose and the ring creeps and frets its seat, too tight and the interference consumes the internal clearance and the bearing runs preloaded.
- Standard: Boundary dimensions are to ISO 355 / DIN ISO 355 / GB/T 297. Quoting the standard on the order guarantees the mounting dimensions are interchangeable between suppliers — it does not standardize load ratings, limiting speeds or internal design, which remain manufacturer-specific.
Mounting & Assembly Practice
- Seat the rollers before measuring anything. Rotate the shaft several full turns under a light load while tightening; unseated rollers give a reading that changes completely once the assembly first runs.
- Set the pair with a dial indicator on the shaft end, or by the tighten-then-back-off procedure the assembly drawing specifies. "Nip it up and add a quarter turn" is not a setting method.
- Allow for the temperature difference in service: a pair set to zero cold can run in preload hot, which is why most industrial and wheel-end applications specify a small residual endplay.
- Press on the cone bore face when mounting the cone, and on the cup back face when mounting the cup. Never press one ring through the rollers of the other.
Common Selection Mistakes with 30300 Series Tapered Roller Bearings
- Assembling to a torque figure alone. Nut torque and bearing setting are related only through friction, and friction on a threaded assembly varies by a factor of two.
- Reusing one half of a set after a failure. Replace both cup and cone, and replace both positions of an opposed pair — a new cone running on a spalled cup fails again quickly.
- Ignoring the assembled width T and specifying to B and C, which leaves the housing spacing wrong by the amount the rollers stand proud of the ring faces.
- Sizing this bearing from the boundary dimensions alone. Load ratings and limiting speeds are manufacturer-specific for this series and are deliberately not published here — take them from the catalog of the bearing actually being supplied and calculate the life against them.
Where 30300 Series Tapered Roller Bearings Are Not the Right Choice
- Never as a single bearing. One row carries axial load one way and unloads entirely in the other, so it must be mounted against another row or against a shoulder that opposes it.
- Not as a floating position. A tapered roller bearing must be located axially by definition; use a cylindrical roller bearing where the shaft has to be free to grow.
- Not for high speed relative to ball bearings. Roller end and rib sliding generates heat, and speed limits are correspondingly lower.
- Little misalignment tolerance — a few minutes of arc. Where the seats cannot be held parallel, use a spherical roller bearing.
- This type will not tolerate misalignment. The rolling or sliding contact is a line, so a fraction of a degree of tilt moves the whole load onto the end of the contact and the stress concentration there is what fails the bearing.
