Listing the most common problems with bottom bracket standards
With all the bottom bracket standards on the market, it is quite shocking that the bicycle industry did not find the one that works perfectly for all applications. At Kogel Bearings we spend a good amount of our day looking at bottom brackets, so I felt it was time to share the pros and cons of all systems with our friends. This information should help you find the bottom bracket and crank combination that best fits your needs.
I’m not here to burn any frame builder for their choice for this or that system, or to push users into a certain direction. Opinions get strong when discussing bottom this problem area of the bicycle, so I have tried to stay objective and Kogel Bearings will keep on striving for the best possible solution given your choice of crank and frame.
BSA-ITA threaded bottom brackets
The good old threaded bottom bracket. Many times on forums people wish they could go back to the days where everything was simple. I argue that it was never simple, with Italian vs BSA, Campy vs. Shimano and all the different spindle lengths, but that’s another discussion.
The world was a better place when everything was threaded? I beg to differ....
The fantastic thing with threaded frames is just that: it’s threaded. The cups lock into place and align themselves. Also the system is very easy to remove and reinstall should there be an issue. All modern day set ups have the bearings running nice and wide, so stiffness is never an issue.
The main down sides of a threaded set up is that not all cranks fit. A true BB30 spindle will be too short to make it through the frame. Another problem is that it is not possible to cut threads into a carbon frame. Any carbon frame will need an aluminum bottom bracket shell glued in, which in itself could be a source of creaking and it is a no no for any designer trying to make the frame as light as possible.
Introduced by Cannondale in the early 2000s, BB30 was supposed to increase crank stiffness with it’s ‘bigger than Shimano’ spindles. While that may be true for a shorter and thicker spindle, my experience is that the narrow set up does the exact opposite: the bearings are so close together that the system becomes unstable and power is lost through flex. This narrow build also ramps up the stress on the bearings.
With the standard being designed to make sure the bearings do not fit too loose in the frame, another common problem is bearing compression. The bearings are pressed into an opening that is too small to fit, which causes the bearings to seize up. With this point and the above mentioned narrow spacing, BB30 bearings are known to have a very short lifespan.
The right side of this diagram shows that the bore diameter for a BB30 shell is 41.96mm with a tolerance of +0.025, which is super tight. In order not to go over the tolerance and have the bearings fit loose in the frame, many manufacturers cut the frames on the smaller side, which causes the bearings to seize up.
On the positive side, if you are looking to ride with a super narrow Q-factor BB30 is your friend.
PF30 was introduced by SRAM as an open standard for anyone to use. It built on the narrow Q-factor of the BB30 but tried to fix a few BB30 issues by pressing the bearings in a cup before they were placed in the frame. The first one is the super tight tolerances that come with a BB30 frame. The PF30 tolerance is four times bigger, which allows the frames to be built with all carbon BB shells. The down side of a larger tolerance is that it is almost impossible to make the cup press perfectly in every frame. Results are creaking and (again) bearing compression, depending where your frame sits in the range.
Bottom brackets have been confusing customers and mechanics around the globe for decades. It does not look as if that is going to change any time soon.
Shimano’s answer to the press fit craze is called simply ‘press fit’, but more commonly known as BB86 for road bikes and BB92 for mountain bikes. It has the wide set up of a threaded bottom bracket and keeps the bearings in a cup similar to PF30. The system is typically very stable and stiff, because there is a wide BB area that the other frame tubes and grab onto.
A minor down side is that the BB86 shell is smaller in diameter than a PF30, so the down tube can be wide but needs to be flattened where it meets the BB shell.
A big issue with the smaller diameter of the Pressfit shell is that it does not accept 30mm spindles very well. The different solutions that are on the market between Rotor, Enduro Bearings, Race Face and our own, show that the jury is still out on how to tackle this problem. Even though I consider the Kogel Bearings solution best in class, I would still advise anyone to stay away from this combo if you can avoid it.
In our next post we will be looking at BBRight, 386EVO and a few other standards before we try to come to conclusions on all these options.
If you have any questions about Kogel Bearings, ball bearings in general or our Ball Bearing Adventures, please ask them either in the comments section below, one of our social media channels or by email via firstname.lastname@example.org. We will answer them in a highly professional, but not always scientific way. We do not shy away from many subjects. Please ask, we are here to answer.