Bottom bracket thoughts on my new bike
Bottom brackets (BB) are like opinions, every bike has one. And opinions about the best bottom bracket seem to vary wildly from one person to the next.
This article is part of a wider series in which I am trying to write down what my experience is with getting a custom made Titanium bike from Waltly in China.
Click here for the main bike page, in there there are also links to each section.
For my new bike I’ve chosen the BSA threaded standard and I’m using a Hope Threaded Bottom Bracket (hopetech.com).
In short: I was doubting on using a press fit BB since that has been working fine on my 2018 Cube Agree former bike. But from what I understand the press fit standard is especially nice when used in carbon frames, since the alignment of the BB cups is more difficult than on a metal (aluminium/titanium/steel) bike.
From what I understand the best BB for a metal bike is threaded. The best BB for a carbon bike is PressFit.
Threaded BB on a carbon bike: why is it difficult
Two problems:
- Left and right shell mis-alignment
- Threading carbon
Alignment: If you look at the picture below you can see the left and right shell. When molding the frame it is easy to have a slight mis-aligment between both shells.
A big voice in exposing BB (mis)alignment is Hambini, and this picture explains somewhat exaggerated what might go wrong with a misaligned BB cup. Hambini roasts a lot, but his point is in general: The bearings will wear out faster when they are not aligned properly. (And he shows a lot of mis-aligned BB’s on his youtube channel)
Press-fit bottom bracket cups are made of plastic and those cups are softer than the bearings and the carbon, thus it forms itself better when the crank is inserted. To be honest, I think it still isn’t perfect and bearing can wear out quick when the alignment is not done properly on a carbon bike. Changing the PressFit BB to another brand (or cup material) is not always the solution since the frame alignment is not solved.
There are options to improve the cup alignment:
Moderate option: Screw in PressFit, the cups are made of aluminium and the cups screw in to each other in the middle, thus improving the alignment. Wheels MFG and Hope create such BB’s
Extreme option: Hambini’s Bottom Bracket. He inserts a full milled aluminum sleeve, thus the alignment is (probably) perfect. It adds a lot of weight though, and costs a pretty penny.
Last resort option when you go through BB’s like crazy and your bikes manufacturer is not helping you when you want to replace the frame.
The next problem; Threading in carbon
You can hardly add threads to carbon. Even if you succeed then you can not put as much pressure/torque on the shells as you would with metal threaded solution. One way to circumvent that is to add an aluminium shell in which you could actually create a thread. But joining aluminium and carbon is at the very least:
- More expensive
- Won’t hold as good as carbon on carbon
- Probably would creak
Thus quite often it sucks.
Metal frames: Why threaded works well
Both alignment and threading issues are negated when you look at the bottom bracket on a metal bike.
As you can see in the picture, the bottom bracket is made from one tube, thus the alignment is already much better then aligning two cups. It can be slightly impacted when the frame is welded (it can warp due to heat) and it’s important that the BB is faced correctly. In general those two issues are no big problem.
Next to that; Threading can be done in the frame material, no bonding necessary.
Conclusion:
As mentioned at the start of the article, I went for a BSA threaded BB, mostly for ease of use and I can find parts easily since it’s such a widely adopted standard.
I chose for the Hope brand mostly due to the weather sealing. Hope is an UK based brand. In the UK they know proper bad weather and I like to cycle year round in all weather.
I don’t really have an opinion on ceramic coated BB’s, other than that they are simply too expensive for me to even consider ;-)