The War of the Stars is raging on the big screen, while the war of standards is raging in the bike industry. Another bottom bracket revolt has just started on bikes. And just like in the movie, a small group of rebels is showing the powers that be the way to go. Who ultimately wins is written in the stars for bicycles.

Adieu press-fit: Chris King and Argonaut Cycles have designed a new bottom bracket standard that combines large diameter bearings and screw-in by thread. The bearing shells on the left, the assembly tool on the right (Image: Argonaut Cycles, Vimeo)

Press fit... and the problem with tolerances
Ben Farver, owner of frame builder Argonaut Cycles, talks straight: "Pressfit 30 is handy for building a frame and letting the customer use any cranks available on the market. The problem with Pressfit, however, is that you have to adhere to super-precise tolerances, both for the frame and the bearing. These tolerances often work against each other."

This is what it looks like in the store workshop
What Farver says looks like this in the store and in the workshop: The customer complains of cracking in the bottom bracket area of his x-thousand franc bike. Not only is the customer dissatisfied, but the mechanic has a lot of swearing to do: a tight-fitting or more than tightly pressed-in press-fit bearing is almost impossible to get out of the frame. The only solution is to brute force the bearing out. This comes with the side effect of possibly damaging the carbon frame - which of course makes the job a lot more fun. And the fun continues, because if the interface in the frame is narrow where the bearing is inserted, it will inevitably crack again, as the bearing is under pressure from the outside and does not run smoothly. Left and right bearing mounts that are not aligned with each other are also very prone to cracking.

And there are other cracking possibilities: If the bearing seat is too wide with a press fit, the bearing or bearing cup will move in the frame - and crack all the more annoyingly. There are said to be manufacturers and mechanics who glue bearings into expensive carbon frames with superglue as an emergency solution to keep things quiet. The removal is then likely to be a lot of fun again, see above.

Who benefits from pressfit bearings?
With the BB30 standard, invented by Cannondale in 2000 with a system integration approach and made available to the bike industry as an open standard, larger-volume bearings were used for the cranks. These can absorb forces better, provide more stiffness in the bottom bracket area and are really light. In principle, these are major advantages. However, the bearings inserted or pressed into the frame are still a big bummer.

Pressfit is often very annoying
Why is press-fit rubbish? For the reasons described above and mentioned by Argonaut Cycles owner Farver. The tolerances are too tight so that there are no fluctuations in large series. The beneficiaries are the frame manufacturers, who can advertise their frames as lighter and stiffer thanks to Pressfit - and no longer have to mount threaded bearing shells in the frame. A frame with a Pressfit mount is cheaper to manufacture than an identical frame with a threaded bottom bracket. If the press-fit bearing does not fit precisely and the bike keeps cracking, the stores can take the blame. A warranty claim due to a cracking bottom bracket can turn into a gauntlet between frame, crank and bottom bracket manufacturers. This is because there are countless frame manufacturers and even more component manufacturers when it comes to bicycles: the fact that they agree on manufacturing tolerances in the tenth of a millimeter range and stick to them is unfortunately an illusion.

Left and center: A bottom bracket shell in T47 format, on the right a comparison with the familiar BSA dimension. (Image: Engin Cycles, via Facebook)

How can it be different? Back to the future!
Farver from Argonaut Cycles thought about the bottom bracket and talked to the bearing specialists at Chris King. The bike enthusiasts wanted to retain the advantages of large bearings, but combine them with a threaded bearing shell screwed into the frame. The idea seems simple and practical. With "Thread Fit 30i", Chris King and Argonaut Cycles present a threaded bottom bracket with a large bearing diameter, which leaves all crank options open. Chris King has worked on the concept with other component manufacturers and is now presenting the "T47" standard, which will be open for use by frame and component manufacturers from 2016.

How does it work?
The frame needs a thread again! This is easy to do with aluminum, steel or titanium frames. For carbon frames, this is also a well-known technique from the times before Pressfit, i.e. before the year 2000 - but it is a cost factor to precisely install a metal thread in the carbon/resin mixture. A thread, correctly fitted and/or cut, is honest, so to speak: there is far less tolerance tolerance here, the bearing can simply be screwed in or not. If the bearing cannot be screwed in cleanly, someone has messed up. With a pressed-in bearing, the situation is far less clear or even invisible.

Quality rebels against the bike empire
It is to be hoped that the quality rebels will show the bike empire where the hammer hangs and the bottom bracket thread will soon strike back. The standard is openly available for 2016, but it will take around 2-3 model years to see which manufacturers jump at the new bottom bracket standard.

A thread doesn't have to be the cure-all, here a completely screwed up bearing shell.

One but remains
However, one small but remains: a bolted bearing interface is not without its difficulties. If the thread is not cut precisely, the thread pitches do not match or the thread grooves have been damaged due to improper assembly or disassembly work, a frame can quickly end up on the scrap heap.