Tag Archives: bottom bracket stiffness

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.

BB30

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

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.

Pressfit (BB86/BB92)

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 info@kogel.cc. 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.

What makes a good bottom bracket a great bottom bracket? Part 2

In part 1 of this blog post, we looked at different bottom bracket types and at adapters. Part two will go a bit more in depth about the best location for bearings and installation techniques.

Bearing stance and bottom bracket stiffness

Imagine the bottom bracket area of your bike to be very similar to the transmission in a car. You can have the strongest engine and the widest tires with the most grip. As long as the parts connecting them are not as stiff as they should be, all that power is not going to result in maximum acceleration.

Bottom bracket stiffness is super important. Besides avoiding plastic and unnecessary parts, you want to look at a bottom bracket with a wide bearing stance. The closer the bearings are to the crank arms, the wider the base for your spindle to rest on. This translates in a stiff set up and speaking from our experience, a lot less wear on the bearings.

bottom bracket adapters
A clear demonstration of a narrow bottom bracket shell mated with a long crank spindle. All the adapter space is wasted real estate. Moving the bearings as far out as possible will increase stiffness and bearing life.

Installation and removal

This is something to consider for any press fit type bottom bracket. Threaded bottom brackets are installed with the appropriate tool and removed with the same.

Installing and removing threaded cups is done with the same tool.

Switch to anything pressed and information is all over the place: instructions range from using Loctite to epoxy to grease or nothing at all. In our opinion, you should think about removing a bottom bracket before installing it: anything glued into the frame is going to leave a residue, which needs to be removed before installing something new. In the case of epoxy, this could mean you spend the next twenty minutes toying with a box cutter or Dremel tool. Kogel Bearings prefers grease for installation. It helps the bottom bracket slide into place, helps to silence potential creaking points and can be cleaned with a rag after removal.

install kogel bearings with grease.
any loctite or epoxy used in a bottom bracket is going to dry out and needs to be removed before the next installation. This can be a time consuming task.

While you are thinking about removing a bottom bracket, have a look on the inside of the cups. Press fit bottom brackets are often removed with a hammer and some sort of punch. Now look on the inside of your cup, is there something your tool can grip on and take a beating if the cups are tight in the frame?

Conclusion

In short, there are many things to consider for a quality bottom bracket:

  • Type: threaded, press fit or threaded press fit, whichever fits best with your frame
  • Materials and small parts: look for a high quality build with as few parts as possible
  • Bearing stance and  stiffness: look for bearings placed as far apart as possible
  • Ease of installation and removal: how easy is it to get the bottom bracket in the frame and how easy is it to remove and prep the frame  for the next bottom bracket

Notice how we did not speak about weight? If you follow all these steps (alu cups, wide stance, quality build), you  will no doubt end up with a bottom bracket that  is a handful of grams heavier than a plastic, narrow  stance  bottom bracket with adapters. In our eyes, there are only a few grams to be saved on a bottom bracket and if choosing those extra grams is going to help you transfer more of your watts to the road, they are well spent.

***

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 info@kogel.cc. 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.