A customer called this week and asked a fair question: why did we spec a T47 bottom bracket on our frames instead of a press-fit unit. Here is the answer in plain language.

What is a T47 bottom bracket?

T47 is a threaded bottom bracket standard. The shell in the frame has internal threads cut at 47mm diameter with a 1mm pitch. The bottom bracket cups thread into those threads, the same way an English/BSA bottom bracket has done since the 1970s, just in a much bigger shell.

The 47mm shell size is no accident. It is effectively a Press Fit 30 shell (46mm internal diameter) with threads added. T47 keeps the wide stance of a press-fit setup and puts threads back into the interface.

Why do threaded bottom brackets work better?

Threaded interfaces work. They have worked for the better part of a century in cycling. A threaded cup engages along the full length of the threads, the torque spec is real and repeatable, and a small amount of preload locks everything in place.

A press-fit cup, by contrast, holds position by interference alone. The cup is slightly bigger than the shell, and you press it in until friction does the work. That holds up when the tolerances on the shell and the cup are both held tight. When either side drifts by even a few thousandths of an inch, the fit goes loose and the noise starts.

That is the noise most riders associate with press fit: the creak under hard pedal load. It is not always a defective bottom bracket. Most of the time it is the cup moving microscopically against the shell because the fit is not tight enough to stop it.

Why do press-fit bottom brackets creak?

A few things have to be true for a press-fit interface to stay quiet for the life of the bike. The frame shell has to be machined to the right diameter, parallel and true on both sides. The bearing cup has to be machined to a matching diameter, parallel and true. The two surfaces have to stay clean, dry, and stable through temperature cycles, water exposure, and repeated load.

Hold all three of those, and a press-fit works fine. Miss any one and you get a creak. The field fix is usually grease, fresh assembly, or in worse cases an adhesive. None of those address the underlying tolerance issue. They just cover it up.

Threaded interfaces take that whole problem off the table. The threads themselves keep the cup in position. You can service the bottom bracket as many times as you want without changing how it fits.

Does T47 sacrifice stiffness compared to press fit?

No. The reason brands moved to press-fit in the first place was stiffness. A 46mm internal diameter shell is wider than the 34mm internal of a traditional English BB. That extra width lets the frame designer use larger-diameter chainstays and seat tubes meeting at the bottom bracket, which makes the rear triangle stiffer for the same wall thickness. More stiffness for less weight.

T47 keeps that win. The shell is the same width as Press Fit 30. You get the same envelope to build a stiff rear triangle around, the same room for big-tube junctions, the same power-transfer benefit.

So you do not trade stiffness to get threads back. You get both.

Will T47 fit my existing 24mm or 30mm cranks?

Yes. T47 is flexible on the crank side. The same shell supports 24mm spindles, 30mm spindles, and 24/22mm stepped spindles, by changing the bottom bracket cups and reducers. A rider can move between cranksets without changing the frame. That matters in BMX racing, where riders run a mix of older and newer cranksets from different brands.

Is T47 easy to service at home or trackside?

We build frames for people who race them, work on them, and ride them for years. Serviceability is part of the spec.

A T47 bottom bracket installs and removes with a standard bottom bracket tool and a torque wrench. No press, no special bushings, no waiting on a shop that has the right driver. When a bearing wears out, the cup comes out, the new unit goes in, and the bike is back together in five minutes.

A press-fit unit needs a press for installation and a bearing puller for removal. Over-press it and you damage the cup. Under-press it and the unit moves. Field service in a pit at a national is harder than it should be.

Why does Supercross BMX use T47 on its race frames?

When we spec T47 on our race frames, we are picking the proven reliability of a threaded interface, the stiffness and power transfer of a wide press-fit shell, the spindle compatibility racers want, and the serviceability our customers count on.

T47 is also an open standard. Any frame builder and any component brand can use it. That open adoption is what makes us comfortable building flagship frames around it. It is not a proprietary spec we control. It is a shared standard with a real future.

Quick Reference — T47 vs Press Fit