How do I identify my BB shell type?

Measure the shell width (68, 73, 83, 86.5, 92 mm) and check if it is threaded or smooth bore. BSA threaded is by far the most common. Press-fit shells are smooth inside.

What is the difference between BSA and Italian thread?

BSA (English) uses 1.370" x 24 TPI with the drive-side cup having left-hand thread. Italian uses 36mm x 24 TPI with both sides right-hand thread. BSA is far more common worldwide.

Are press-fit bottom brackets problematic?

Press-fit BBs can creak if not installed properly. Many cyclists prefer threaded standards (BSA or T47) for reliability. T47 is a newer threaded standard that fits press-fit shell bores.

How often should I replace my bottom bracket?

A quality BB lasts 10,000-20,000 km depending on conditions. Replace when it feels rough, makes clicking noises, or has noticeable play. Clean and inspect annually.

Can I use a Shimano crankset with a SRAM frame?

Yes. BB compatibility depends on the frame shell and crankset spindle, not the groupset brand. Use the correct BB for your crankset spindle diameter and frame shell type.

BikeCalcs

Bottom Bracket Calculator — Find the Right BB

Find the right bottom bracket for your frame and crankset combination.

BB Shell Type

Crankset Type

How We Calculate This

Bottom Bracket Compatibility

BB shell determines the physical size and thread type
Crankset determines the spindle diameter and BB interface
The correct BB connects your frame shell to your crankset spindle
Common spindle sizes: 24mm (Shimano), 28.99mm (SRAM DUB), 25mm (Campagnolo), 30mm (BB30)

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.