Bottom Bracket Bearing Sizes: BB30, PF30, BB86, BB90 & BMX
A bottom bracket has three different size references: the frame shell, the crank spindle and the bearing cartridge. Identify all three before searching for a replacement. BB30, PF30 and BB86 are assembly or frame-system labels, not interchangeable bearing part numbers.
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Measure the frame, spindle and bearing as separate parts
For a cartridge bearing, d is the bore, D is the outside diameter and B is the width. For a frame, record the shell bore and the distance between its faces. For the crank, record the bearing-seat diameter and whether it changes between the two sides.
Example: a conventional BB30 arrangement can use a 30×42×7 mm 6806 cartridge. In a conventional PF30 arrangement, a cup carries that cartridge in a 46 mm frame bore. The 46 mm number describes the frame interface; it is not a request for a 46 mm outside-diameter cartridge.
Do not measure over a plastic reducer and label that reading as the steel bearing bore. Photograph the removed parts in order and retain the original complete marking, including suffixes.
Frame-interface lookup: BB30, PF30, BB86, BB92 and BB90
These are identification dimensions, not manufacturing tolerances. Widths below describe the listed common arrangements; frame-specific variants still require their own documentation. Type a standard, measurement or feature to narrow the table instantly.
7 reference rows. Filters apply as you type.
On smaller screens, scroll the table sideways to read all columns.
| Frame/system | Shell interface | Typical shell width | Bearing arrangement / next check |
|---|---|---|---|
| BB30 | 42 mm bore | 68 or 73 mm | Direct cartridge; classic 30 mm-spindle version uses 6806. |
| PF30 | 46 mm bore | 68 or 73 mm | Bearing in removable cup; identify the cup and spindle variant. |
| BB86 / BB92 (PF41) | 41 mm bore | 86.5 mm road; width variants for MTB | Press-fit cups; the name alone does not define the cartridge size. |
| Trek BB90 / BB95 | 37 mm bore | 90.5 / 95.5 mm | Direct bearing seats; confirm crank-specific kit and frame condition. |
| BSA / English | 1.37 in × 24 TPI thread | Commonly 68 or 73 mm | Threaded cups; drive-side thread is left-handed. |
| Italian | 36 mm × 24 TPI thread | 70 mm | Both cups have right-hand threads; not a BSA substitute. |
| T47 | M47×1 thread | Model-dependent | Threaded interface; not the unthreaded PF30 system. |
No verified row matches these filters. Clear a field to widen the reference; an empty result does not prove that a part does not exist.
BMX: American, Mid, Spanish and Euro are not the same size
A query for a 19 mm BMX bearing specifies only one measurement. Mid, Spanish and Euro parts can address different frame interfaces even when the crank bore is the same. Do not order from spindle diameter alone.
On smaller screens, scroll the table sideways to read all columns.
| BMX system | Frame-side identifier | What must still match |
|---|---|---|
| American / Ashtabula | Approximately 51.5 mm pressed cup | Cup, crank and loose-ball/caged-bearing arrangement. |
| Mid | Approximately 41.2 mm direct cartridge OD | Spindle bore, bearing width and internal spacer. |
| Spanish | 37 mm frame bore | 19 or 22 mm spindle version and bearing width. |
| Euro | BSA threaded frame interface | The particular cup set and crank spindle; not a universal 19 mm cartridge. |
Is Mid the same as BB86 because both are close to 41 mm?
No. The nominal Mid cartridge outside diameter and the PF41 frame-and-cup interface describe different components. Similar rounded numbers do not establish fit.
Does an older Raleigh use ordinary BSA cups?
Not necessarily. Some older Raleigh three-speed frames use 1.37 in × 26 TPI rather than 24 TPI. Check the actual thread before choosing a cup; the bicycle name does not identify the bearing-ball diameter.
Cartridge, external, sealed and square-taper: what the labels tell you
External or outboard describes where the bearing-supporting cups sit relative to the frame. Sealed describes protection, not a common diameter. A cartridge may mean an individual sealed bearing or a complete bottom-bracket assembly containing bearings and an axle; establish which component a catalogue is naming.
Square taper identifies a crank-to-axle connection. It does not by itself identify a replaceable cartridge bearing, loose-ball size or service procedure. Likewise, MTB and road describe applications, not one universal bottom-bracket size.
What size are BB86 or BB92 bearings?
The frame interface is 41 mm, but the internal bearing depends on the complete bottom bracket and crank. One verified example is Wheels BB86/92-BB for a 24 mm spindle, with SB-24X37-1 cartridges measuring 24×37×7 mm. That example is not a rule for every PF41 assembly.
Can I use a 6805 instead of a dedicated 24 mm bearing?
Do not infer interchange from the series number. Compare the complete cartridge dimensions and the presence of any reducer with the exact assembly specification; use the model reference rather than a rounded spindle measurement.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Frame bore and shell width | Identify the frame interface first. | Measure the bare shell, not an installed cup or dust cover. |
| Bearing d×D×B | Record the cartridge bore, outside diameter and width separately. | Adapters, extended inner rings and seals may change the installed envelope. |
| Crank spindle | Record diameter, steps and the complete crank model. | A 24 mm crank does not prove that every bearing under its cover has a 24 mm bore. |
A practical investigation sequence
Identify and record
Record the bicycle, frame year, crank model, bottom-bracket marking and drive/non-drive positions before dismantling.
Check the context
Separate frame dimensions from cartridge dimensions in your notes. Record any reducers, retaining rings, cups and covers.
Verify before acting
Use the standards table to identify the interface, then use the model table to compare a named bearing or service kit.
Keep the decision traceable
Keep the exact assembly instructions with your measurements. A dimensional candidate is not a manufacturer-approved substitution.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
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Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- Wheels Manufacturing bottom-bracket standards — Exact named component and stated dimensions or procedure scope only. Collected 2026-10-01. No universal fitment, repair approval or independent performance result is inferred.
- Park Tool bottom-bracket standards and terminology — Exact named component and stated dimensions or procedure scope only. Collected 2026-10-01. No universal fitment, repair approval or independent performance result is inferred.
- Wheels SB-6806-1 / Enduro 6806 record — Exact named component and stated dimensions or procedure scope only. Collected 2026-10-01. No universal fitment, repair approval or independent performance result is inferred.
- Wheels BB86/92-BB assembly record — Exact named component and stated dimensions or procedure scope only. Collected 2026-10-01. No universal fitment, repair approval or independent performance result is inferred.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.