Ask A Mechanic: Bottom Bracket Standards

Phillip wants to know: What are the pros and cons of the different bottom bracket standards like BB30, PF30, BBright, etc.

The explosion of new bottom bracket standards in recent years has created plenty of headaches for mechanics everywhere. While they were all developed with the best of intentions, the implementation of many of them have been far from trouble-free.

I’m just a mechanic, not an engineer, so I can’t speak to the design benefits of the various standards, but I can tell you about my experiences with each of these. Before we get into the much-maligned new standards, it’s instructive to take a look back at the challenges the English bottom bracket has, as this is the standard that each of the new standards intended to improve upon.

It was not uncommon to have to chase the threads of an English bottom bracket shell and then face the shell in order to remove any excess paint and to ensure that the faces were square. These bottom brackets creaked too, so before you go claiming that the English bottom bracket was perfect, you should remember that thousands of mechanics earned their living working on them. With all that said, it is definitely the easiest standard to use from a mechanic’s perspective and I definitely prefer to work on bikes with this standard over all others.

BB30 has largely gone away, and I’m happy about that. This standard used bearings that pressed directly into the frame that rested against a circlip that is fitted to internal grooves in the bottom bracket shell. The clips were weak and they creaked. If the bearings fit tight enough to stay put, they often were compressed to the point that they didn’t spin freely. If they spun freely, they usually ended up creaking and moving around.

PF30 is an improvement on BB30 that utilizes a flanged cup for the bearing to sit in. That cup is then pressed into the frame. The cup helps to keep the bearing in place while preventing unwanted movement. The downside of this standard is that the aluminum crank spindle sits right on the steel inner bearing race, the same as BB30, which causes spindle wear and eventually leads to creaking. If the standard was meant to include a plastic sleeve like those found on English bottom brackets utilizing a 24mm spindle, it would be better in my opinion.

Unfortunately, the worst part of the PF30 standard hasn’t been the standard at all, it’s been the poor manufacturing tolerances that the industry has used on bikes with this standard. Pressed in headsets see way bigger loads applied to them, yet they always seem to fit right no matter how much the bike costs and almost never creak or come loose. There is no reason why the industry couldn’t do the same thing with bottom brackets.

BBRight is very similar to PF30 and uses the same bearings and cups, they are just spaced further apart. It never caught on in the industry and for some reason seems to suffer from the same crank wear and sloppy frame tolerance issues that PF30 does.

BB86 and BB92 are the smaller diameter, wider spaced pressfit standard. My experience is that these seem to work better than PF30, in spite of the fact that they function in essentially the same way as PF30. I think this just proves my earlier point that maintaining tight tolerances is the solution we need the industry to adopt.

I don’t have anything against adopting new standards for bottom brackets or any other component interface for that matter. I just feel that the industry just needs to either commit to tighter tolerances or choose standards that don’t require such tight tolerances to work properly. A standard that takes installation and removal procedures and tools into account would also be greatly appreciated. No one should have to use a hammer to install or remove anything on a carbon frame. Leave that kind of stuff to the BMX world where it belongs.

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