Bottom Bracket Size Chart: Find Your Bike's Perfect Fit

The bottom bracket is the heart of your drivetrain. It’s where the crankset spins, turning your effort into forward motion. If you pick the wrong size, you’re looking at persistent creaking, premature bearing failure, and, in the worst cases, permanent frame damage. Modern bikes mix standards like a cocktail, so one must check manufacturer specs before buying anything. This bottom bracket size chart is your defense against buying parts that don’t fit. Save the PDF or print it out for your workshop wall.

Decoding Common Bottom Bracket Standards

You’ve got two main families: threaded and press-fit. Threaded systems, like BSA or ITA, screw directly into the frame. They are reliable and easy to service, but they demand that you check your shell width—typically 68mm for road or 73mm for mountain bikes. If your shell is 73mm, you’ll often need to remove spacers meant for 68mm setups to get the chainline right. Get this wrong, and your front shifting will suffer.

Press-fit systems, like BB30 or BB86, rely on interference fits. The bearings sit directly in the frame shell. These designs allow for wider, stiffer spindles—usually 30mm—but they demand precise tolerances. If your frame's internal diameter is even a fraction of a millimeter off, you’ll be chasing creaks for the life of the bike. According to industry engineering standards, shell diameters must be measured with digital calipers to ensure the bearings aren't forced into an ovalized or undersized bore.

Quick Reference: Shell Dimensions

Standard	Shell ID (mm)	Shell Width (mm)	Type
BSA	34.8 (Threaded)	68/73	Threaded
BB30	42	68/73	Press-Fit
PressFit 30	46	68/73	Press-Fit
BB86	41	86.5	Press-Fit

The catch is that shell width dictates crank spindle length. If you try to jam a road crank into a 73mm mountain shell, the spindle won't reach the non-drive side bearing. It won't work.

Navigating the Specs: How to Read the Data

The chart breaks down your frame by the shell diameter and width. One must identify your frame's internal bore first. For instance, if you measure a 46mm internal diameter, you’re looking at either a PF30, BBRight, or BB386EVO setup. The difference lies in the width—PF30 is standard at 68mm or 73mm, while BBRight pushes out to 79mm. Don't guess. Pull out your calipers and verify the shell ID before you order parts.

The spindle diameter column is your next stop. This defines what crankset you can actually install. If your frame uses the 41mm ID associated with BB86, you are locked into a 24mm spindle crank—like most Shimano Hollowtech II models—or specific DUB options. You can't force a 30mm spindle into a 41mm bore. It won't fit.

Field Observations and Common Pitfalls

I see bikes in the stand every week where someone tried to force a press-fit bearing into an undersized shell. If the shell ID is 42mm, you're working with a BB30 standard. If you try to shove a 46mm PF30 cup in there, you’ll crack the frame. It happens faster than you think. Always check the technical specifications provided by your frame manufacturer.

• The SRAM DUB Trap: DUB isn't a shell standard. It's a 28.99mm spindle. You need a DUB-specific bottom bracket that matches your frame's shell, whether it’s threaded BSA or press-fit PF30.
• The ITA Threading Warning: Italian (ITA) shells have a 36mm diameter. Unlike the common BSA standard, both sides tighten clockwise. If you treat it like a BSA shell, you’ll strip the threads on the drive side.
• Asymmetric Widths: The BBRight standard uses a 79mm width. This is wider than a standard 68mm road shell. Standard cups will leave you with a loose crankset and poor chainline.

Handling Edge Cases

Sometimes your measurement falls between the numbers. If you measure 46.1mm on a shell intended for 46mm, your frame might be worn or out of tolerance. Press-fit systems demand that you ensure a tight, secure fit; if the bearing slides in by hand without resistance, the shell is likely damaged. You can save this chart as a PDF or print it to keep at your workbench for quick verification when you’re mid-build. Never assume a "standard" is universal across different model years—manufacturers change specs without warning. When in doubt, measure twice and buy once.

Troubleshooting Compatibility Issues

When parts don't want to play nice, you’ve got options. Adapter kits from reputable brands like Wheels Manufacturing allow you to run 24mm cranks in 30mm shells. But they aren't magic. If you feel excessive lateral play or notice binding while spinning the cranks, back off. Forcing a tight fit often ruins the bearings or, worse, scores the frame's bore. If the cups don't seat with firm, consistent pressure, stop. Take it to a local shop. A professional mechanic has the press tools to confirm if your shell is within the ISO tolerance standards.

Spindle and Bearing Cheat Sheet

Spindle Diameter	Common Standard	Bearing Type
24mm	Shimano / Hollowtech II	Cartridge (Steel/Ceramic)
28.99mm	SRAM DUB	Cartridge (Sealed)
30mm	BB30 / PF30	Cartridge (High-Load)

You can save this PDF version of our bottom bracket size chart to your phone or print it out for your workshop wall. Keeping this reference handy saves you from ordering the wrong parts during a late-night build. Most sealed bearings last about 2,000 miles, but wet weather riding demands that you check for grit sooner. If you hear grinding, it's already too late.

Common Questions

• How often should I service my bottom bracket? Every 2,000 miles is a safe bet, though muddy conditions require more frequent cleaning.
• Can I mix ceramic and steel bearings? You can, but it’s a waste of money—match your bearing type to your riding goals.
• Why does my bike creak? It's usually a dry press-fit cup or a loose threaded shell; clean, grease, and reinstall.
• Is a 30mm spindle always better? It’s stiffer, but it leaves less room for large, durable bearings in some frame designs.

Measure twice. Buy once. Keep your drivetrain quiet.