from Rookie’s keyboard
Hello, friends
Today, I will share another observation of mine regarding bottom brackets.
I’ve always been direct when it comes to bike topics and will just say it – I don’t like press-fit bottom brackets.
Why? Keep reading, and you will find out.
But because I want my posts to be maximally complete. I will start with the pros of press-fit BBs.
The Pros of Press-fit Bottom Brackets
1. No Need To Thread The Bottom Bracket Shell
Since press-fit bottom brackets are pressed into the frame, there’s no need to thread the bottom bracket cups and the bottom bracket shell. The simplified production process saves money and time.
Another benefit of the press-fit mechanism is that the absence of threads eliminates the possibility of cross-threading the bottom bracket and ruining the frame and/or the cups.
Also, there is no need to worry about the thread type (French, English…etc.) since there isn’t any.
Therefore, at least in theory, press-fit bottom brackets could be compatible with a great number of frames. In practice, however, this doesn’t happen because the vast majority of frames are still designed for a threaded bottom bracket.
The Disadvantages of Press-fit Bottom Brackets
Tight Tolerances to Satisfy
Ideally, press-fit bottom bracket cups are easily installed with a press but are also completely immobile once in the bottom bracket shell.
To achieve this task, manufacturers have to work within tight tolerances. The term tolerance refers to external dimensional accuracy, machining accuracy, and running accuracy.
If the bottom bracket is ever so slightly larger than needed, it will be difficult or even impossible to press-fit it into the frame. Conversely, if its diameter is too small, the bottom bracket won’t be secure.
Consequently, both the frame and the bottom bracket have to be machined to perfection. To make this a reality, the manufacturers have to invest more money in production and quality control.
Bottom Bracket Shell Wear
Frames with a carbon bottom bracket shell experience wear because carbon isn’t an ideal material for bearing support. As a result, the bottom bracket shell opens up and the bottom bracket is no longer secure.
In some cases, the user won’t even have to press-fit the bottom bracket anymore as it will slide into the shell right away.
The aftermath of this phenomenon is an unstable bottom bracket spinning inside the bottom bracket shell. The friction between the bottom bracket body and the frame will destroy both the frame and the bottom bracket.
To fight this issue, manufacturers have advised users to cover the bottom bracket cups in epoxy to prevent the bottom bracket from sliding inside the frame. The purpose of the epoxy wasn’t to glue the bottom bracket to the frame but to fill the gap created by the bottom bracket shell wear.
High Maintenance
To minimize the chance of malfunction, users have been known to invest extra care involving:
- Frequent inspections of the bottom bracket
- Regular servicing
- Application of securing compounds such as Locktite…etc.
While those measures have a positive effect, one cannot help but ask the question – is all that effort worth it?
At the end of the day, threaded bottom brackets create none of those issues and work just fine for a great number of miles.
New Tools Needed For Installation/Removal
To install or remove a press-fit bottom bracket the user will need an extractor and a press. The tools are not incredibly expensive, but they’re still an expense that has to be taken into consideration.
If later the user decides to return to a threaded bottom bracket, the tools will be obsolete. Also, bike tools do not hold their price on the second-hand market well.
Miniscule Weight Gains If Any
One of the main incentives behind press-fit bottom brackets was to reduce “redundant weight”.
How so?
The bearings of threaded external bottom brackets are press-fitted into the bottom bracket body. Then, the cups are threaded inside the frame.
The goal of press-fit bottom brackets was to eliminate the middle man and press-fit the bearings directly into the frame.
However, the saved weight is too small to matter and of no benefits to recreational riders.
The table below compares the weight of threaded (external BBs) and press-fit BBs.
| Press-fit | Weight | Threaded | Weight |
|---|---|---|---|
| FSA Pressfit PF-30 | 79g | Shimano SM-BBR60 | 77g |
| SRAM PF41-86-GXP | 62g | Token BSA-68-DUB | 120g |
| SRAM PF46-68/73/79/86.5/92-30 | 130g | e*thirteen 68mm | 90g |
| e*thirteen PF46-68/73/83-30 | 94g | SRAM GXP Team | 106g |
| Hope PF41-86.5/89.5/92-24 | 112g | Shimano Deore SM-BB52 | 88g |
| KCNC BB92 PF41-89.5/92-24/KTYPE | 93g | Shimano Tiagra BB-RS500 | 92g |
| Shimano SM-BB71-41C | 72g | SRAM DUB 70mm-Italian | 75g |
| FSA BB86 PF41-86.5-24 | 82g | e*thirteen 83mm | 94g |
| Easton Cinch PF41-86.5-30 | 82g | Shimano SM-BB71-41A | 72g |
| SRAM PressFit BB92 GXP | 90g | Shimano XTR SM-BB93 | 73g |
| Shimano SM-BB71-41B | 70g | Shimano Deore XT BB-MT800 | 82g |
| Average | 87.8g | Average | 88g |
Conclusion: The average weight of press-fit and threaded bottom brackets is extremely close. Therefore, the theoretical weight savings that press-fit bottom brackets offer are minimal.
Short Bearing Lifespan
If the calculations are off even slightly, the bottom bracket will assume an angle over-stressing the bearings. The aftermath is a shorter bearing life.
More Difficult To Service
The tools needed to install a basic threaded bottom bracket can be found at virtually every bike shop.
Also, the process is a lot more straightforward and comes with greater room for error.
Riders have also expressed animosity towards press-fit bottom brackets for the following reasons:
- Frequent creaking even when the bike is new.
- Press-fit BBs can’t be removed frequently without altering the fit and thus creating stability issues later on.
- Press-fit bottom brackets are not as light as some cyclists believe.
- Press-fit bottom brackets do not fix a problem nor do they improve the rider’s performance. Thus, the reason for their existence is highly questionable, especially in the segment of recreational riders.
- Poor quality control. Some riders don’t experience major problems while others would gladly avoid a bike that’s otherwise awesome simply for having a press-fit bottom bracket. This indicates that the quality control is not consistent.
- Threaded bottom brackets have worked just fine for decades.
The Return To Threaded Bottom Brackets
The fact that some top brands have returned to producing high-end bikes with threaded bottom brackets indicates two conclusions:
- They’re listening to the complaints of the riders.
- Producing a press-fit bottom bracket that creates zero issues is possible but takes too much effort for the advantages that it offers. Thus, in some cases, it’s wiser to abort the mission.
In conclusion
For every person who is happy with their press-fit bottom bracket, you will find 10 who would like to put theirs in a hydraulic press.
That said, the technology itself isn’t the main problem. Press-fit bearings can work very well, and the idea behind the system is solid. One example would be the headset. Most bikes, even the retro models, use press-fit headset cups that rarely creak and create issues.
However, when it comes to bottom brackets, it’s more difficult to satisfy the requirements needed to produce a unit that is durable, economically viable, and with consistent quality across the entire line-up.
For now, threaded bottom brackets continue to offer solid performance, easier installation, fewer chances of creaking and a greater bearing lifespan all while weighing about the same as their press-fit rivals.
I have a road bike produced in 1987 that still uses its original square taper bottom bracket. I haven’t heard a single creak from it despite losing count of the bike’s mileage. The bottom bracket itself costs USD 5.
Meanwhile, there are people in group rides with expensive bicycles with press-fit bottom brackets that creak like a broken musical instrument. Understandably, the owners of those machines are a little underwhelmed that their high-end purchases are underperforming in that regard.
Until next time,
Rookie
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