BMX Bottom Bracket Standards — Threaded vs Press-Fit, Euro and T47
Supercross BMX Engineering · Apple Valley, California
Threaded vs Press-Fit: The Bottom Bracket Nobody Reads
It is one line on a spec sheet, it is the cheapest thing on a frame to get wrong, and it decides whether your bike is silent in three years or creaking at every gate.
Euro / BSA Mid T47 Press-Fit Threaded Since 2001
We built our early frames on a press-fit shell. We built press-fit prototypes again in 2007. We built Mid BB frames for a factory rider. Every time, the threaded shell won. This is the engineering behind that — including the parts where press-fit is genuinely cheaper to make, Mid genuinely has a bigger bearing, and a press-fit frame can genuinely be stiffer on the day you buy it.
The short answer
A threaded bottom bracket will outperform a press-fit bottom bracket over the life of the frame. Euro (BSA) is the long-standing standard and it works. T47 is the best interface in cycling right now, because it keeps the threads while taking the larger shell diameter that lets you run bigger bearings and a stiffer 30 mm spindle.
Press-fit standards — BB86, BB92, BB30, PF30, BB386, and Mid — are a cheaper way to build a frame. That is not an insult, it is a manufacturing fact, and it is the whole reason they exist. Whether that trade is worth it to you is the point of this page.
What each one actually is
Press-fit
A press-fit shell has no threads at all. It is a smooth bore, and the bearing cups are pressed into it as an interference fit — the cup is very slightly larger than the hole, and friction alone holds it there.
For a factory this is attractive, and honestly so. You skip the threading operation. You skip facing and chasing the shell afterward. On a carbon frame you avoid bonding or moulding a threaded metal insert into the layup, which is a real cost and a real failure point of its own. Fewer machining steps, less tooling, faster throughput.
Threaded
A threaded shell has cut threads, and the cups screw in. Euro (BSA) is a 68 mm wide shell with 1.37" x 24 TPI threads. T47 uses the same thread pitch in a much larger 47 mm diameter, which is where it gets interesting — that is roughly the internal diameter of a press-fit shell, with threads cut into it.
Why press-fit creaks
The failure is not a defect. It is the design working exactly as designed, in the real world.
An interference fit depends entirely on the shell being machined to a tight tolerance and staying at that tolerance for the life of the frame. Two things work against that. First, tolerance stack: the shell, the cup and the bearing each have their own manufacturing window, and those windows add up. Second, materials move. Aluminum and carbon expand and contract at different rates with temperature, and both flex under load — and a bottom bracket shell sits at the single highest-load junction on the entire frame, taking your full gate start through the cranks.
Here is the part that matters. When a press fit loosens by a fraction of a millimetre, there is nothing to tighten. There is no thread, so there is no preload to take up the slack. The cup moves microscopically against the shell under every pedal stroke, and that movement is the creak. Your options are shims, retaining compound, an adapter, or a new frame. None of those is a repair — they are all ways of living with it.
A threaded shell has an answer to the same problem, and the answer is a torque wrench. Preload is set on assembly. If it works loose you tighten it. If the threads get damaged a shop chases them and the frame carries on. It can be serviced in a parking lot at a national with tools that fit in a small bag.
"But isn't press-fit stiffer?"
Sometimes, yes. Let us deal with this properly, because it is the strongest argument the other side has and it is usually answered badly.
A press-fit shell is typically wider in diameter than a traditional Euro shell. A wider shell takes a bigger bearing. A bigger bearing makes room for a fatter spindle — 30 mm instead of 24 mm or 22 mm. And a fatter spindle is stiffer in torsion, because stiffness rises very steeply with diameter. So a frame built around a wide press-fit shell can absolutely be stiffer at the bottom bracket than a frame built around a narrow threaded one. Anyone who tells you otherwise is selling you something.
But look closely at where that stiffness actually comes from. It comes from the diameter of the shell. It does not come from the absence of threads. Threads never made a bottom bracket flexible — a narrow shell did. Press-fit and the wide shell arrived together historically, so the industry got into the habit of crediting one for the other.
Which is exactly what T47 proves. Take the wide shell that gives you the big bearing and the 30 mm spindle, and cut threads into it. You keep every bit of the stiffness argument and you get the torque wrench back. The stiffness was never the thing you had to trade away — and once T47 existed, nobody had to trade it.
And the part almost nobody says out loud: a creak is a stiffness failure
Stiffness figures are measured on a new frame, in a fixture, on a good day.
Think about what a creaking bottom bracket physically is. It is a cup moving against a shell. That is a joint with play in it, at the highest-load junction on the bike, and every bit of that movement is pedal input going into the frame instead of the rear wheel. A loose interference fit is not a stiff interface. It is a slightly loose one making a noise about it.
So the stiffness advantage a press-fit frame has on day one decays into a stiffness deficit the moment the fit moves — and there is no thread to take that movement back out. A threaded shell that has held preload for four seasons is stiffer, at the point of use, than a press-fit shell that went slightly loose in season two. The spec sheet will never tell you that, because the spec sheet is a photograph of the frame when it was new.
The question that settles it
If a brand tells you their bottom bracket is stiffer, ask three things: what test, what number, and against what?
A stiffness claim without a test method and a figure is an adjective. Everyone's frame is stiff. Nobody's marketing department has ever described a frame as adequately stiff. Across this category you will find a great deal of writing about stiffness and almost no published bottom bracket stiffness data with a stated method — not from us either, and we will say so plainly rather than pretend.
What we do publish is the number we can stand behind: our carbon frames are tested to three times the EN BMX safety requirement, and the method is written up in the carbon engineering whitepaper. A standard, a multiple, and a document. Ask whoever you are buying from for theirs, in the same form. How readily that comes back tells you more than the adjective did.
We built the alternative. Twice.
It is easy for a brand to say it prefers threaded. We tested it, with real frames and real riders, and came back to the same answer both times.
In 2007 FSA pushed us to build press-fit, and we built prototypes. FSA was making the cranks and bottom brackets for BB30 and promoting the standard hard across the industry, and press-fit was being sold to every manufacturer as the future. On our end that meant actual frames, actual shells, actual riding — not a drawing.
It is worth understanding why a component company, rather than a frame company, was the one in our shop. Cannondale developed BB30 and then released it as an open standard in 2006 — no licence, no royalty, anyone could build to it. That is the best thing that can happen to a parts manufacturer. Every frame built to BB30 was a frame that needed BB30 cranks and BB30 bearings, and there was no gate on selling them. Cannondale gave away the shell; the money moved to whoever made the parts that went inside it. So the people evangelising press-fit to frame builders were rarely frame builders themselves.
We also built a small run of Mid BB ENVY frames for Kris Fox during his time on our team. Mid is a press-fit shell, and it has a real advantage that deserves saying out loud rather than being quietly left off a comparison: a Mid shell takes a bigger bearing than a Euro shell. That is exactly why the freestyle side of the sport adopted Mid and still runs it. Bigger bearing, more surface, longer life under the kind of load a freestyle bike sees. It is not a marketing story; it is a genuine engineering gain over Euro.
Which is the clearest way to understand BB30, if you came up through BMX: BB30 was the Mid bottom bracket of the road and race market. Same idea, same promise — a bigger bearing in a wider shell — and the same catch, which is that you give up the threads to get it. It did not solve the problem then and it does not now.
Both times, the threaded shell won anyway — decided on frames we had built and riders we had on them, not on theory.
Cannondale invented BB30 and made it an open standard in 2006. Cannondale's current flagship SuperSix Evo is back on a threaded BSA shell.
Why T47 is the king
For years the choice felt like a compromise. Euro threads gave you serviceability but a narrow shell. Press-fit and Mid gave you a wide shell with room for big bearings and a 30 mm spindle, but no threads. T47 ends the argument by taking the wide shell and cutting threads into it.
| Euro / BSA | Mid | Press-fit (BB86, BB92, BB30, PF30, BB386) | T47 | |
|---|---|---|---|---|
| Threads | Yes | None | None | Yes |
| Preload adjustable | Yes, torque wrench | No | No | Yes, torque wrench |
| If it loosens | Tighten it | Shim, glue or replace | Shim, glue or replace | Tighten it |
| Damaged threads | Chase and carry on | No threads to repair | No threads to repair | Chase and carry on |
| Bearing size | Limited by shell diameter | Bigger than Euro | Large shell, room for 30 mm | Large shell, room for 30 mm |
| Stiffness when new | Good | Very good | Very good | Very good |
| Stiffness in year three | Same — re-torque it | Falls if the fit moves | Falls if the fit moves | Same — re-torque it |
| Cheaper to manufacture | No | Yes | Yes | No |
| Serviceable trackside | Yes | Not really | Not really | Yes |
The tell that settles the argument
Chris King builds the most respected bearings in cycling. Their reputation rests on bearing life and nothing else. They named their entire bottom bracket range ThreadFit — and that range includes a ThreadFit 30, whose specific purpose is to put a threaded interface back into a shell sized for press-fit, alongside a ThreadFit T47.
A company that lives and dies on whether bearings stay quiet engineered its way toward threads, not away from them, and built a product to retrofit threads into frames that shipped without them. That is not a marketing position. That is where their engineering budget went.
What we run, and the year we changed our minds
It would be easy to leave this next part out, and a lot of brand pages would.
The original Supercross cro-mo frames used an American bottom bracket — a press-fit shell, and the standard of the day. Nearly every US-built BMX frame ran one. It is what the parts bin supported and what everybody knew, and we built that way like everybody else.
In 2001 we introduced the threaded Euro shell on the UL series, and we have never gone back. Every Supercross frame since has been threaded. That is twenty-five years of the same decision — tested twice since, and upheld twice.
We did not arrive at threaded out of principle. We arrived at it having built both, ridden both, and listened to both.
Bill Ryan · Founder, Supercross BMXBottom bracket standards come and go. BB30 arrived as the future. PF30 arrived as the fix for BB30. Both have largely left the race side of the sport. A threaded shell has outlived every one of them, and it will outlive the next one too.
| Frame | Bottom bracket |
|---|---|
| Vision F1x — carbon | Threaded T47 in Pro and larger · threaded Euro 68 mm in Expert XL and smaller |
| Vision F1 — carbon | Threaded T47 in Pro and larger · threaded Euro 68 mm in Expert XL and smaller |
| 2026 ENVY RS7 — aluminum | Threaded T47 in Pro and larger · threaded Euro in Expert XXL and smaller |
| Vision RSX — aluminum | Threaded Euro, every size |
| SX450 — chromoly | Threaded Euro |
The reason the big sizes get T47 is straightforward: that is where the power is. A Pro XXXXL rider putting a full elite gate start through the cranks is loading that junction harder than anyone, and T47 gives that rider the biggest bearing surface and the fullest thread engagement we can build. Smaller frames run threaded Euro because it keeps weight down for a lighter rider who does not need the larger shell, and it is still threaded.
How to check what you are buying
Four questions, and any brand should answer all four immediately.
One: is the shell threaded or press-fit? If the spec says BB86, BB92, BB30, PF30, BB386 or Mid, it is press-fit. If it says BSA, Euro, 68 mm threaded or T47, it is threaded.
Two: does it change by size? This one catches people out. Several frames on the market ship a threaded Euro shell in the small sizes and switch to press-fit in the Pro sizes — which means the riders making the most power are the ones without threads. Ask for the spec of the size you are actually buying, not the spec at the top of the page.
Three: if it creaks, what is the fix? On a threaded frame the answer is "torque it." If the answer involves compound, shims or an adapter kit, you have learned what you needed to know.
Four: if they claim it is stiffer — what test, what number, against what? A stiffness claim with no method and no figure is an adjective, and every frame ever built has been described as stiff by the people selling it.
Frequently asked questions
Is a threaded bottom bracket really better than press-fit?
Over the life of the frame, yes. Both can be built well, but a threaded shell takes adjustable preload from a torque wrench, can be re-tightened when it loosens, and can have its threads chased if they are damaged. A press-fit shell has none of those options, because it has no threads — once the interference fit loosens, there is nothing to tighten and the fixes are shims, retaining compound or a new frame.
Isn't a press-fit bottom bracket stiffer?
It can be, and that is a fair claim rather than marketing. Press-fit shells are usually wider in diameter, a wider shell takes a bigger bearing, and a bigger bearing allows a 30 mm spindle, which is stiffer in torsion than 24 mm or 22 mm. But that stiffness comes from the shell diameter, not from the absence of threads — threads never made a bottom bracket flexible, a narrow shell did. T47 takes the same wide shell and cuts threads into it, so you keep the stiffness and get the torque wrench back. And remember that stiffness figures are measured on a new frame: a creaking press-fit shell is a joint with play in it at the highest-load junction on the bike, which is a stiffness failure by definition, and there is no thread to take that play back out.
Why do brands use press-fit if it is worse?
Because it is cheaper and faster to manufacture, and that is a legitimate engineering trade rather than a trick. A press-fit shell skips the threading operation, skips facing and chasing, and on a carbon frame avoids bonding a threaded insert into the layup. It also allows a larger shell diameter for bigger bearings and a 30 mm spindle, which was its original selling point — though T47 now delivers that without giving up the threads.
Is a Mid bottom bracket better than Euro?
Mid has one genuine advantage over Euro: it takes a bigger bearing, because the shell is wider. That is why freestyle adopted Mid and still runs it, and it is a real engineering gain rather than marketing. The catch is that Mid is press-fit, so it gives up adjustable preload and thread repair. T47 settles it — you get the bigger bearing of a wide shell and you keep threaded cups, which is why our Pro and larger frames run T47.
What was BB30, and why did it fade?
BB30 was the Mid bottom bracket of the road and race market — a wider press-fit shell offering a bigger bearing and a 30 mm spindle. Cannondale invented it and made it an open standard in 2006, which meant any component manufacturer could build cranks and bearings for it without a licence, so the parts industry promoted it hard. It ran into the same problem every press-fit interface runs into: no threads means no adjustable preload, so once the fit moves it creaks and there is nothing to tighten. Cannondale's current flagship SuperSix Evo is back on a threaded BSA shell.
What is the difference between Euro (BSA) and T47?
Both are threaded and both use a 1.37" x 24 TPI thread pitch. Euro is a 68 mm wide shell at a smaller diameter. T47 uses a much larger 47 mm diameter, roughly the internal size of a press-fit shell, which makes room for larger bearings and a stiffer 30 mm spindle while keeping full thread engagement. Euro is the standard; T47 is the better interface where the rider is putting down serious power.
Which bottom bracket standards are press-fit?
BB86, BB92, BB30, PF30, BB386 and Mid are all press-fit — the bearings or cups press directly into an unthreaded shell. The older American shell found on many vintage US-built BMX frames is also a press-fit design. BSA, Euro 68 mm and T47 are threaded.
Can a creaking press-fit bottom bracket be fixed permanently?
Usually not permanently, because the underlying cause is a fit that has loosened and there is no thread to take up the slack. Shims, retaining compound and threaded-insert adapter kits all manage the symptom, and some manage it well for a long time. A threaded shell removes the problem instead of managing it — which is why Chris King, a company whose reputation rests entirely on bearings, sells a ThreadFit 30 designed to put threads back into a press-fit-sized shell.
What bottom bracket does Supercross BMX use?
Threaded. The original Supercross cro-mo frames used an American press-fit shell, which was the standard of the day, and in 2001 we moved to the threaded Euro shell on the UL series. Every frame since has been threaded — including through press-fit prototypes built in 2007 and a small run of Mid BB ENVY frames for a factory rider, both of which lost to threaded. Today the Vision F1, Vision F1x and 2026 ENVY RS7 run a threaded T47 in Pro and larger sizes and a threaded Euro shell in the smaller sizes; the Vision RSX is threaded Euro in every size, and the SX450 is threaded Euro.
Every frame we build is threaded
T47 where the power is, Euro everywhere else, and no press-fit shell on a Supercross frame since 2001.
Related reading: the carbon engineering whitepaper covers Toray fiber grades, monocoque construction and our 3× EN BMX safety margin. Our 2026 BMX race frame guide compares the whole field, including which frames use which bottom bracket.