TechnicalBike

Bottom bracket standards: BSA, PF30, BB86, T47 — the complete guide

Max

|4 minMarch 11, 2026

Bottom bracket standards: BSA, PF30, BB86, T47 — the complete guide

Why so many standards

The bottom bracket (BB) is the part that connects the crankset to the frame. The problem: the cycling industry has never managed to agree on a single standard. The result, in 2026, is that you face a dozen different standards. Some are excellent. Others have caused millions of creaks.

Here are the four standards you'll encounter most often, with their strengths, weaknesses, and when they cause trouble.

BSA — the classic threaded standard

Shell diameter: 34.8 mm (1.370" x 24 TPI)
Width: 68 mm (road) or 73 mm (MTB)
Type: threaded (the BB screws into the frame)

Advantages:

The most reliable and easiest to maintain
Unscrew, clean, regrease, screw back in — no press, no adhesive
Tolerates minor frame alignment imperfections
Easy and inexpensive to replace

Disadvantages:

Requires a threaded frame shell — impossible on monocoque carbon frames without an insert
Limited width (68/73 mm) that constrains lateral stiffness

BSA is the recommended standard for any cyclist who values peace of mind. If your frame is BSA, don't change a thing.

PF30 (Press-Fit 30)

Shell diameter: 46 mm
Width: 68 mm (road) or 73 mm (MTB)
Type: press-fit (cups are pressed into the frame)
Axle: 30 mm

Advantages:

Wider shell = ability to stiffen the frame in that area
30 mm axle stiffer than the traditional BSA 24 mm
Design freedom for carbon frame manufacturers

Disadvantages:

Creaking — this is the number one problem with PF30. Carbon frame manufacturing tolerances vary, and pressed cups can develop micro-metric play. Result: tick-tick-tick with every pedal stroke.
More complex replacement (requires a press and an extractor)
Sensitive to water and dust ingress

If your frame is PF30 and you have creaking, the first thing to do is remove, clean the frame shell, apply Loctite 641 (retaining compound) on the cups, and reinstall. Often, that's enough.

BB86 (Press-Fit 86)

Shell diameter: 41 mm
Width: 86.5 mm (road) or 89.5/92 mm (MTB)
Type: press-fit
Axle: 24 mm (Shimano) or adaptable to 30 mm

Advantages:

The most widespread standard on road and carbon MTB bikes since 2010
Natively compatible with Shimano (24 mm axle)
Stiffer frame thanks to the wider shell

Disadvantages:

Same creaking issues as PF30, especially with imprecise frame tolerances
Requires adapters to fit a 30 mm axle crankset (SRAM DUB, for example)

Shimano designed BB86 for its Hollowtech II cranksets. If you run Shimano on a BB86 frame, compatibility is native and installation is straightforward.

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T47 — the best of both worlds

Shell diameter: 47 mm
Width: 68 mm (road) or 85.5 mm (MTB)
Type: threaded (like BSA, but wider)

Advantages:

Threaded = no press-fit creaking
47 mm diameter compatible with 30 mm axles (SRAM DUB, Praxis) and 24 mm (Shimano with adapter)
Increasingly adopted by high-end manufacturers (Allied, Argonaut, Factor, Canyon on select models)
Maintenance as simple as BSA

Disadvantages:

Still a newer standard — fewer BB choices than BSA or BB86
Requires a frame designed for it (no conversion from PF30 or BB86)

T47 is the rising standard. If you're buying a new frame and have the choice, go T47. You'll get threaded reliability with modern axle compatibility.

How to identify your standard

Not sure which BB you have? Here's how to check:

Look at the frame — the shell diameter is often engraved or on a sticker
Measure the inner diameter of the empty shell (without the BB):
Check if it's threaded: run your finger inside — if you feel threads, it's BSA or T47