Are All Bike Bottom Brackets The Same Size? | Not Same

That’s because frames and cranks use a mix of standards. Size isn’t only one number. You have to match shell width, shell inner diameter, thread type or press fit, and the crank’s spindle. Get those four right and the parts slide together and run quiet.

Are All Bike Bottom Brackets The Same Size?

The short answer many riders hope for is “yes,” but the reality is “no.” A bottom bracket is a system that ties a frame’s shell to a crank’s spindle. Two frames can share the same width and still need different parts if one is threaded and the other is press fit. Two cranks can share the same brand and still need different cups if one uses a 24 mm spindle and the other uses a 30 mm spindle. That mix is why riders keep asking the same question.

Bottom Bracket Sizes By Standard

Use this quick map to see how the common standards differ: name, width, and shell type with typical inner diameter or thread.

Standard	Shell Width	Shell Type
BSA / English	68 mm (road), 73 mm (MTB)	Threaded 1.37"x24 TPI
Italian	70 mm	Threaded 36 mm x 24 TPI
T47	68, 73, 86.5 mm	Threaded M47x1.0
BB30	68 mm (road), 73 mm (MTB)	Press fit, 42 mm ID
PF30	68–73 mm	Press fit, 46 mm ID
BB86 / BB92	86.5 mm (road), 89.5–92 mm (MTB)	Press fit, 41 mm ID
386EVO	86.5 mm	Press fit, 46 mm ID
BBRight	79 mm	Press fit, 46 mm ID
BB90 / BB95 (Trek)	90.5 mm (road), 95.5 mm (MTB)	Direct fit, 37 mm ID

Sizing Basics That Prevent Noise And Wear

Shell Width

Shell width is the left-to-right length of the frame’s bottom bracket shell. Road frames often land at 68 mm or 86.5 mm. Many mountain frames are 73 mm, 92 mm, or 95.5 mm. T47 can appear in 68, 73, or 86.5 mm. Match the number on your frame before you shop.

Shell Inner Diameter And Thread Type

Threaded shells use a screw-in cup. The common English spec is 1.37"x24 TPI with left-hand thread on the drive side. Italian shells use 36×24 and thread the same direction on both sides. Press fit shells have a smooth bore where cups or bearings press in, so the inner diameter matters more than any thread. BB30 uses a 42 mm bore. PF30 is 46 mm. BB86/92 uses 41 mm. BBRight sits at 46 mm.

Crank Spindle Diameter

Now look at the crank. Shimano Hollowtech II uses a 24 mm spindle. SRAM GXP uses 24/22 mm. DUB is 28.99 mm. Many 30 mm cranks ship with BB30 or 386EVO setups. The match between spindle and bearing is non-negotiable.

Close Variant: Bike Bottom Bracket Sizes And Fit Rules

Not all frames accept every crank. A PF30 frame can run a 24 mm crank with the right adapters, but it won’t take a 30 mm crank if the cups don’t leave enough inner clearance once sealed. A BB86 frame wants 41 mm press cups for the spindle you run. A BSA frame needs the right threaded cups for the spindle.

How To Identify Your Frame’s Standard

Check The Specs

Frame makers list shell width and type on the product page or manual. If your frame came complete, look up the model year and build. You’ll usually see a line that reads like “BSA 68 mm,” “PF92,” or “BB30.”

Measure With Basic Tools

Pull the crank. Wipe the shell faces. Use a ruler or calipers to read the width. Then read the inner diameter. A 46 mm bore points to PF30 or T47 (before threading). A 41 mm bore points to BB86/92. Threads point to BSA or Italian. If the bearings sit directly in carbon with no cups, you may have BB90/95.

Use A Trusted Reference

You can cross-check your measurements against a Park Tool standard guide. Wheels Manufacturing also keeps a clear bottom bracket standards chart with shell widths and inner diameters that match each label.

Popular Combos That Work

BSA Shell With 24 mm Spindle

This is the classic road and gravel mix. Pick threaded cups for 24 mm spindles and a width that matches the frame for most builds.

PF92 Shell With 24 mm Or DUB

PF92 uses a 41 mm bore. You can run 24 mm spindles with press-in cups, or a DUB unit sized for 28.99 mm.

T47 Shell With 24 mm, 30 mm, Or DUB

T47 gives the security of threads with the room of a large bore. Cup makers offer versions for 24 mm, 30 mm, and DUB in the common shell widths.

PF30 Or BB30 Shell With 30 mm Crank

These shells were built around 30 mm spindles. With the right cups and seals they spin smooth and keep a low Q-factor.

Brand-Specific Shells

BBRight and BB90/95 are brand-specific fits. BBRight is a wide road shell used by Cervélo. BB90/95 presses bearings into a 37 mm bore molded into select Trek frames.

Crank Spindles And What Fits

Spindle diameter drives bearing choice. Use this table to see common diameters and the bottom brackets that tend to pair with each.

Spindle Type	Nominal Diameter	Compatible BB Examples
Shimano Hollowtech II	24 mm	BSA 68/73 cups, BB86/92, PF30 with adapters, T47-24
SRAM GXP	24/22 mm	BSA GXP cups, BB86/92 GXP, PF30 GXP, T47-GXP
SRAM DUB	28.99 mm	DUB for BSA, PF92, PF30, BBRight, T47
BB30 / 386EVO Cranks	30 mm	BB30, PF30, 386EVO, T47-30
Square Taper (JIS/ISO)	~17 mm spindle flats	BSA or Italian cup-and-cone or cartridge
Campagnolo Ultra-Torque	25 mm halves	BSA/Italian cups, PressFit-UT

Why So Many Sizes Exist

Frame makers balance stiffness, tire and chainring clearance, and build speed in the factory. A wider shell buys room for large tubes and fat tires. A large bore lets designers use big bearings or short axle spacers. Threaded shells ease service. Press fit can save weight and give more internal room.

Choosing The Right Bottom Bracket For Your Build

Start From The Frame

Write down shell width, inner diameter, and whether it’s threaded or press fit. That narrows the field.

Match The Crank

Pick cups or bearings that match the spindle. If you run a 24 mm crank, buy parts for 24 mm. If you run a DUB crank, buy DUB.

Mind The Small Details

Seal types, preload rings, and torque targets matter. Many creaks trace back to dry faces or loose cups, not the standard itself. Grease the shell faces, use the right tools, and tighten to spec.

Brand Notes And Verified Dimensions

Shimano sells a threaded unit marked for 68/73 mm shells that mates with 24 mm Hollowtech II spindles. SRAM’s DUB line uses a 28.99 mm spindle and offers cups for BSA, PF92, PF30, BBRight, and T47. Trek’s BB90/95 frames press 37 mm OD bearings directly into a 90.5/95.5 mm shell. Cervélo’s BBRight is 79 mm wide with a 46 mm bore.

If you want a single page to cross-check those numbers, the Wheels Manufacturing chart lists shell widths and bores for nearly all current labels. Park Tool’s guide maps those labels to the tools and procedures that fit them. Those two references cut guesswork.

Common Mistakes And Easy Fixes

Buying By Brand Name Only

Don’t assume that two cranks from the same brand share a spindle. Read the spec on the arm or spindle, then buy cups to match.

Forgetting About Spacers

Threaded setups often ship with spacers that set chainline and preload. Leave them out and the bearings load badly. Add extras and the axle pinches the seals.

Pressing Cups Dry

Press fit parts seat better with a thin layer of the grease the maker recommends on the bore and cup. Clean the faces, press straight, and check alignment.

Chasing Silence With Random Adapters

Adapters work best when they come from a brand that lists the exact frame shell and crank spindle you run. If the part looks universal, skip it.

Answering The Big Question

So, are all bike bottom brackets the same size? No. Standards vary on width, inner diameter, thread type, and spindle size. Once you identify those numbers for your frame and crank, the path gets simple. Pick a unit that matches both sides and the rest of the build falls into place.

Quick Checklist Before You Order

• Frame shell width measured and written down.
• Frame shell inner diameter confirmed.
• Threaded vs press fit confirmed.
• Crank spindle diameter confirmed.
• Spacers and dust shields laid out per diagram.
• Correct tools on hand for install and preload.

Use a trusted reference like the Park Tool guide or the Wheels Manufacturing chart while you shop. That five-minute check saves returns and keeps the ride silent.